Greetings. Help me figure out why my computer won't turn on.

Computer Specs
Custom Built
AMD X2 4600+
Asus A8N-SLI (socket 939, nForce4 SLI)
Thermaltake 560 W PS
4GB DDR 3200 (4 x 1GB) RAM
9800GT Video Card
RAID 0 (2 x 1TB) SATA (boot volume)
RAID 0 (2 x 80GB) SATA (data volume)
120 GB PATA
CD/DVD Burner
Floppy

History
The computer was working normally when it presumably entered a sleep state after a period of inactivity. When I went to arrive the computer from sleep state, there wasn't any response.

Symptoms
The computer doesn't do a damned thing. Pressing the power switch has no effect.

Actions To Date
Jumping Green wire to Black wire on 24-pin cable from power supply causes power supply to spin up.

Asus A8N-SLI motherboard was replaced with a used board removed from a working system. Symptoms persisted with replacement motherboard.

Manually bridging the power pins on the motherboard with a screwdriver had no result.



Help me figure this one out TWW. I'm running out of ideas.

[Edited on March 7, 2011 at 11:09 PM. Reason : more info]

3/7/2011 11:09:09 PM

Update
I took a multimeter to the power supply while I used a wire to jump greeen to black. All the pins on the 20-pin cable reported what seemed to be their correct voltages. The same was true of the 4-pin 12V cable and the random 4-pin molex I checked as well.

3/8/2011 2:40:48 AM

Try it with one stick of ram. If that dont work try it with another. It just occurred to me but maybe it is booting but the video card is toast and therefore looks like its not powering on. Do you have another you can try?

3/8/2011 6:33:54 AM

I would try a second power supply, just test the mobo and see if it posts.

3/8/2011 10:22:24 AM

^^ I would think that even if the power supply is toast, the PSU and CPU fans and whatnot would still spin up.

^ I'm working on obtaining a different power supply from a friend to see if that will make a difference.

Actually, I have another computer and I'm going to try and use the power supply from the non-working system in the working one. The power supply in the working-system doesn't put out enough wattage to handle the video card in my non-working system.

3/8/2011 11:55:20 AM

Update
Power Supply didn't work when I moved it to a different known-working system. It's looks like it is the culprit. I find it odd that it seems to work when I use a jumper wire to turn it on. Anyone know what that could be about?

3/8/2011 1:51:22 PM

not being tested under load.

3/8/2011 2:54:05 PM

Can you or someone else clarify what effect load would have with respect to the ability of the power supply to acknowledge the power-on signal?

3/8/2011 4:45:58 PM

It could be a signaling problem, but my guess was that the efficiency of the unit simply degraded to a point that it didn't have the necessary power to POST your system. It's not that it's "dead", rather that it's not providing enough juice to get everything going.

Of course I don't have a degree in EE, I just fix computers. I've seen the problem before where a tester says it's good but it won't power on a known-good system.

3/8/2011 11:04:06 PM

Recently I had a computer where this lead was shorting out either on the Mobo or the wires themselves. Exact symptoms described.

I also had an 800w OCZ PSU that would POST on a super cheap mini-ATX board, but would not power my main PC even with minimal load. RMA'd the PSU and was back in business.

I would try the other working power supply without your video card and see if it posts. (use a cheap PCI card or something). Or find a sufficient known PSU to power your main rig whichever is easier.

3/8/2011 11:24:02 PM

Final Update
A new OCZ power supply from Intrex did the trick.

3/9/2011 12:48:41 PM