# New PSU - Computer won't start



## MagnusOpium (Apr 26, 2014)

Hi guys, first time posting here, so be gentle 

I just got done putting a new Corsair CX750M (not great I know, but it'll have to do for now) in my rig, flip the switch, hit the power button and..... Nothing!

I'm certain everything's connected as it should be, and there's a green light on the MOBO just above the SATA ports which vanishes when I flick the backplate switch to the 'off' position and shows up again when I flick it back to 'on'. But when I hit the power button on the front, it just doesn't boot up.

I've tried plugging to old power supply back in and seeing if that works, but the blue power light at the front of the case lights up for about half a second and then vanishes. No noise or movement from anything else.

I've double, triple and quadruple checked all my connections, and everything looks absolutely right. I've tried disconnecting all but the motherboard/CPU/RAM and still nothing. Any ideas?


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## Megabite (Apr 5, 2008)

Howdy,

It could be a faulty power supply ..but you would have to try it on another PC or try a known working power supply on that one to be sure.

All the power connectors to the motherboard are connected the long rectangular one and the other separate one correct?

What happened to make you change the Power supply?


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## MagnusOpium (Apr 26, 2014)

Megabite said:


> Howdy,
> 
> It could be a faulty power supply ..but you would have to try it on another PC or try a known working power supply on that one to be sure.
> 
> ...


Hi  Well I changed PSU due to a GPU upgrade. Old PSU has the wattage but not enough amps on the 12v rail to cope with my new GTX770, so I've upgraded to one that provides some extra wattage (750 rather than 570) as well as providing 62A on the 12V rather than the previous 32A.

Last night the old PSU was firing up just fine, but cutting out whenever the load presumably got too much. As I said, today the old PSU get's me about half a second of the power light coming on and that's all. The new PSU doesn't even give me that.

Yes, the connectors are where they should be. The 24-pin in the 24-socket and the 8-pin in the "EATX12V" socket. Have also checked the power button connector is attached to the correct placve on the MOBO like a dozen times 

EDIT: Just in case it makes a difference, here's my specs:

MOBO: Asus P8Z68-V Pro; 
CPU:Intel Core i5 2500k; 
RAM: 8GB (2x4GB) 1600MHz DDR3 Corsair Vengeance 1.5v; 
GPU: MSI GTX 770 Twin Frozr OC Edition 4GB; 
OS: Windows 7 64-bit;


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## Megabite (Apr 5, 2008)

Understood..... I have a similar motherboard and use the corsair 750 with the GTX 760 GPU.

Have you tried taking your Video card out and re-setting the Ram in the board. I mean to try it with the video cards out Is it possible you moved something when installing the PSU.

It also could be a problem with the motherboard


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## MagnusOpium (Apr 26, 2014)

Yep, I've taken everything not necessary out. I've reseated the RAM and I've tried it with just one RAM stick (tried both seperately) in case one had somehow got corrupted. 



Really hoping it's not a MOBO issue as my Win7 disc is a single-use license, and changing MOBO means having to reinstall windows, right? I've already ploughed £370 into the PC this weekend


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## Megabite (Apr 5, 2008)

When I replaced my PSU I did not need to touch the power switch cables....did you have to on yours?


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## MagnusOpium (Apr 26, 2014)

You mean to the case power button? No, never touched it, certainly never unplugged it, just thought it a good idea to check it was correctly seated in case it'd come loose while I was getting the other cables in place. Would hate to be asking anyone for help after overlooking something that simple. The shame!

A quick update, I just tried the (probably stupid) "paperclip method" and the (new) PSU seemed to power up ok (although it was even quieter than I'd expected) so I'm guessing the MOBO is the problem


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## Megabite (Apr 5, 2008)

How did you use the paper clip method....on the Case switch...or how?


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## MagnusOpium (Apr 26, 2014)

Disconnected the PSU from everything in or related to the PC. Plugged it into the wall, stuck the paperclip into the green and one of the blacks of the 24-pin cable and switched the PSU on.


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## Megabite (Apr 5, 2008)

Understood..... still could the switch on the computer case I would try that next...as that is where most try the paper clip method.

As you are getting a green light on the motherboard I would assume it is getting the correct voltage from the PSU.


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## MagnusOpium (Apr 26, 2014)

I don't understand... What do I do with the paperclip and the case?


EDIT: Just found this on the Antec website (as my case is an Antec 300): 

"Find the Power On/Off Soft Switch wires that connect from the Power On/Off Soft Switch to the Motherboard. Remove the 2pin connect which reads Power/On. There should be 2 male pins expose after the removal of connector. Using a screwdriver. Cross the two male pins with the screwdriver and the computer should start up. If the computer does not start when shorting the 2 expose pins then you have a Motherboard issue. Contact the manufacturer of the Motherboard for possible replacement. If the Motherboard did start then the Motherboard successfully past the test and you need to replace the Power On/Off Soft Switch, which resides in the front bezel of the Rack Mount Case"

I guess that is what you were referring to. Gave it a try and she booted straight up. Looks like the issue is somewhere between the power button and the power button MOBO connector. If I move my reset button wire to the power button connector for now, will I then be able to power up with the reset button?


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## Megabite (Apr 5, 2008)

Yea it basically by passes the PC case switch.....so it sounds like it is just the case switch or loose wire. PC case switches are cheap.

As for the reset button I believe it only switches on and makes a connection when pushed


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## MagnusOpium (Apr 26, 2014)

is it not the same with the power button then? I mean after firing it up with the screwdriver, it stays running after I take the screwdriver away....


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## Megabite (Apr 5, 2008)

If it works then that's fine.....glad it wasn't the motherboard or PSU......so just get a PC case switch

Have you tried it with the Video card in and does it run fine?


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## MagnusOpium (Apr 26, 2014)

Just gonna put it back together now and see what happens.


EDIT: Nope. Put it all back together and it's not starting up. Not even the screwdriver method's working this time 


EDIT EDIT: Tried pulling out the 3 modular cables I had plugged in (1 with 2x8-pin powering GPU, 1 with molexes powering 3 case fans, 1 powering HDD and optical) and then went through plugging each back in and.... apparently the GPU and drives will run fine, but as soon as I plug in the cable attached to the 3 case fans, the machine refuses to power on.

Any ideas about that?


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## metallica5456 (Apr 1, 2013)

It IS POSSIBLE for a BRAND NEW PSU (even a Corsair) to be DOA. I would RMA it and get another one Corsair WILL RMA it free of charge to you.


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## crjdriver (Jan 2, 2001)

Are you using the Q-connector for the case leads? If so, every one of those I have ever seen fits very loose and is easily dislodged.

I have the gen3 version of that board and it has a pw button on the mb itself. Normally this is used for bench testing, etc. You can see if it will pw ON with the button. Note if you have an older ver of the board, it may not have this option.


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## MagnusOpium (Apr 26, 2014)

crjdriver said:


> Are you using the Q-connector for the case leads?


Nope, straight onto the MOBO. I shall have to get a replacement power switch, find out how to attach it, and hope that works. Don't see why it wouldn't.

As for the fans problem, I've pulled the connector off of the MOBO's "cha_fan_1" and not boots up fine, full power, fans spinning away, whole thing seems to be running as it should. So what's the problem there? faulty cable? fans deciding they don't want to speak to the MOBO any more?


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## Megabite (Apr 5, 2008)

If there is any way you can test that PSU on another PC would tell us a lot.

Did you have a problems like this on the other PSU...like problems sometimes with the on/off switch on the PC case?


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## MagnusOpium (Apr 26, 2014)

Megabite said:


> If there is any way you can test that PSU on another PC would tell us a lot.
> 
> Did you have a problems like this on the other PSU...like problems sometimes with the on/off switch on the PC case?


No, not in however long I've been using it. But as I said, when I tried hooking it back up to the old PSU after I couldn't get the new one working, that wouldn't start up either, just a brief flash of the power light, nothing else.


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## Megabite (Apr 5, 2008)

To test the power switch is working correctly would be to test it with a MultiMeter.

It seems strange you are having all these problems now.

As I said using the new PSU or even the old PSU on another PC would tell us something.

When you say fans you are talking about Case fans not CPU fans?


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## MagnusOpium (Apr 26, 2014)

Megabite said:


> To test the power switch is working correctly would be to test it with a MultiMeter.
> 
> It seems strange you are having all these problems now.
> 
> ...


Correct. 2x120mm and 1x140mm case fans. All Antec. They don't seem to be the problem themselves though. Everything's running fine now I disconnected them from the MOBO. Not really sure what advantage I get from having them attached to the MOBO anyway, but I'm 99.9% sure they were connected before the PSU swap, and working.

I don't have a multimeter or another PC. could pop into B&Q and see if they stock multimeters...


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## Megabite (Apr 5, 2008)

If you do not use a Multi meter often then not worth spending the cash...and B&Q are rubbish for that and don't see any on their site. Maplins would be better.

Was there any time when you installed the new PSU in correctly?


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## MagnusOpium (Apr 26, 2014)

Megabite said:


> If you do not use a Multi meter often then not worth spending the cash...and B&Q are rubbish for that and don't see any on their site. Maplins would be better.
> 
> Was there any time when you installed the new PSU in correctly?


Well I guess I'll have to go to Maplins or similar tomorrow to get a new power switch so I'll see how much their multimeters are then.

I can't really think _how _a PSU could be installed incorrectly tbh. It's not rocket science


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## Megabite (Apr 5, 2008)

Understood...

I'm not sure though that it is the new PSU although it could be....but then you say the old PSU isn't working now either (but it could have just died)

You could always take or send the new PSU back for replacement


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## MagnusOpium (Apr 26, 2014)

Megabite said:


> Understood...
> 
> I'm not sure though that it is the new PSU although it could be....but then you say the old PSU isn't working now either (but it could have just died)
> 
> You could always take or send the new PSU back for replacement


To clarify, both PSUs appear to be working absolutely fine so long as I don't plug the case fans into the MOBO. It seems kind of bizarre to me, but there you go


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## Megabite (Apr 5, 2008)

And they were plugged into the MB before and worked ok?


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## MagnusOpium (Apr 26, 2014)

I'm 99.9% sure they were plugged in, and yep, everything ran fine. Now, if I plug them into the MOBO nothing powers up at all.


Just had a thought: In the new setup all three fans are running off the same lead (has 3 molex connectors that reach the right spots of the case) whereas in the old setup one of the fans (probably the front one) was running off of a different lead. The front fan also has it's own 3-pin connector plugged into the MOBO, whereas the other 2 do not. So it may be causing a problem as the front fan is essentially being plugged into the MOBO twice simultaneously. Gotta rush to the shop, but when I get back I will try:

A. Running the front fan from a different power lead, and plugging the rear and top fans back into the MOBO.
B. Keeping all three fans running from the same lead, plugging that lead into the MOBO and unplugging the front fan's own MOBO connector.

I'll do both of those and report back.


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## crjdriver (Jan 2, 2001)

A quick test of the pw switch is to use the case leads for the reset switch. Plug those into the pw switch pins on the board and hit the reset switch. If it pw ON fine, then you know it is the switch and or leads. If you still have problems, it is not the switch. The chance of both switches [ON and Reset] failing at the same time would be astronomical.


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## MagnusOpium (Apr 26, 2014)

crjdriver said:


> A quick test of the pw switch is to use the case leads for the reset switch. Plug those into the pw switch pins on the board and hit the reset switch. If it pw ON fine, then you know it is the switch and or leads. If you still have problems, it is not the switch. The chance of both switches [ON and Reset] failing at the same time would be astronomical.


Yup, switches on from the reset switch no problem. Also, considering in over two years I've never used the reset switch (forgot it even existed tbh) I may as well not bother going out of my way to get a new power switch, and just use the reset to boot up from now on.

Now to try out the stuff with the fans I mentioned in my previous post...


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## crjdriver (Jan 2, 2001)

It is ok to use the "Reset" switch as a pw switch [they are almost always the exact same part] I would consider ordering a new switch and replacing it the next time you have the system apart. Note if you are thinking about upgrading the case, then that would fix the issue as well.

For now it looks like you have it fixed AND saved some money :up:


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## MagnusOpium (Apr 26, 2014)

Well neither of the things I tried changing with the fans worked, but at least everything runs fine when I have them all running off the same molex cord and just don't plug it into the MOBO. Somehow doesn't seem right, but it works so that'll do for now.

I tried using the reset button to turn it on, but got sick of it after about 2 goes as the reset button on the Antec 300 is stupidly narrow and has to be pushed quite far in, it needs a screwdriver to get it down. So I've just been out and got a new reset switch (tried 3 independents who had nothing and Maplins who only had resets, no powers) and hooked that up where the power switch is supposed to go, so that's basically sorted. The fans thing shall have to remain a mystery. For now I'm just glad to have a system that (apparently) works properly 

I probably will swap case sometime over the summer, as the Antec 300 has virtually no cable management going on. I really like the look of the Corsair Carbide Air 540 but there's no way it'd fit on the shelf under my desk, so I'll most likely end up with the 500R...


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## Megabite (Apr 5, 2008)

Well your getting there....I have the CoolerMaster Case which has three fans, a very large one on top of the case. All run from molex connectors. As for my CPU cooler I have a Corsair H80i liquid cooler.

The Cosair 500R case looks fine


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## crjdriver (Jan 2, 2001)

Yes, modern cases have very nice cable mgt. I am typing this on a system using a coolermaster 922; very nice case with good cable mgt. With the cables behind the mb tray, the inside almost looks like nothing is connected ie just the board in the case. Even the sata cables go behind the tray all in all I have to say this is one of my favorite cases.


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