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Let me first start by saying that I searched for other questions that matched my situation and I wasn't able to find any.

So, here's my issue:

Sometimes, when I turn on my desktop, it does not properly power on. I can see that the CPU warning light is on.

Other times, when I power on, the GPU warning light is on when my computer boots, and the screen does not work.

The way I remedy this is by opening up the desktop, flipping the switch on the power supply, and holding down the power button on the mobo until I hear the click of the power discharging. I then switch back on the PSU, wait a few seconds, and then hit the power button on the mobo. Sometimes this works, other times, it just causes the GPU problem to trigger and I have to start the process over again.

Here is the relevant equipment I'm using:

PSU: Corsair Professional Series Gold High-Performance 1200-Watt Power Supply CMPSU-1200AX

Motherboard: ASUS P8Z68-V PRO Motherboard

Video Cards: EVGA GeForce GTX 570 Superclocked 1280 MB x2 in SLI

So, is it my PSU, or might it be my MOBO?

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Just to be sure: You have this after powering Off, or after leaving your computer unattended for a long time? (ie, what you describe could be just some kind of "sleep mode") –  Olivier Dulac Jul 5 '13 at 16:36
    
After Shut Down. Never after Restart or waking from Sleep. And Hibernate is disabled on my machine, so not sure about that. –  Christopher Rayl Jul 10 '13 at 20:21
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3 Answers

If you don't have much technical knowledge I highly recommend you taking the PC to a professional lab or even consulting with a friend who has the sufficient knowledge.

And for the answer itself:

  • Check all the connections on the motherboard, it is possible some detached wires are causing this problem (read the MOBO / PSU guide before!).
  • Clean dust from the PC - even if all the connection on the MOBO are fine, some dust may be blocking on on-board power (not likely, buy I have seen such case before).
  • Try using another PSU. Also try replace the MOBO with another computer's MOBO - just for testing.
  • If the MOBO is fine (according to the previous step) then the PSU is damaged, and vice-versa.
  • If you have successfully identified the problem just replace the broken component.

If none of the above steps helps, I (again) recommend taking the PC to a professional lab.

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First of all ASUS has a probe utility. ASUS Probe II V1.00.29 for Windows XP/Vista/7 32bit & 64bit. Also part of the AI Suite.

Launch the probe and have it monitor your voltages. Launch a benchmark like 3dmark even the demo version. When the 3dmark is complete look at the graph do any of the voltages dip below 5% of the correct voltage? The 12v channel is not supposed to go below 11.4v ever. If you have a decent PSU it should not go below 11.9v. Check the 5v,3.3v, and other voltages.

Make sure your bios is up-to-date and all your drivers.

If any of the voltages are even close to 5% to low it is the power supply.

You mentioned your GPU is superclocked also, it maybe overclocked a bit too high. If 3dmark freezes your computer you may want to lower the overclock slightly to see if that helps.

Have you overclocked you CPU also?

Modern PSU like yours have independent rails. That is each rail has independent power so you can overload rail 1, but have plenty on rail 2. A 1200w PSU like yours usually has at least 5 rails. If your voltages are low you maybe able to resolve the issue by using different power plugs because they are on different rails.

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I have not, though the mobo has a Turbo Boost switch or some such that is supposed to automagically OC the CPU. –  Christopher Rayl Jul 5 '13 at 15:39
    
@ChristopherRayl While your running ASUS Probe II also check the temperature graphs. –  cybernard Jul 5 '13 at 15:56
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As @matan129 says, you can try replacement of the parts to see which one fails. I would also try replacing the graphics card with a low-grade one, to see if it is failing or if the power is insufficient for both Mobo and Graphical card. Shops that sell parts have usually free testing facilities. A related question here has an answer with howto's for testing power supplies. good luck.

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