Computer Power Issue - Doesn't seem to be the power supply.

[stewie-Y]

Hello everybody.

I have a computer here that I was asked to fix, and was told that it wouldn't turn on. When I brought it home and first turned it on, it booted up with no problem, and thought that there was no problem. But, the next day it would not turn on. So, I swapped out a different PSU that I knew worked, but the computer still wouldn't turn on. I was testing different things with the computer plugged into a power outlet and sitting on my lap, and all the sudden I noticed that it had just gotten power, so I hit the power button and it booted up fine. Since then I haven't been able to get it to power up again, though.

As of right now, the computer will not boot up, and only has one yellow light light on the motherboard which is the "AUX PWR" light.

Any help would be greatly appreciated, thanks!

[Geek-9pm]

Well....the "AUX PWR" light means power is coming from the wall to the computer.
You have already tried another PSU. Some now it seems it just might be the power button itself.
The power button on modern PCs does not really send power to the system. Instead, it is a way to get the system to pay attention and start the power on sequence.
But it might be another issue. Here is some ideas from another forum
http://www.tomshardware.com/answers/id-1716963/erratic-startup-behavior-power-power-power-needed-boot.html

Remove/check/swap the fans connected to the motherboard, especially the one on the CPU fan header, I've seen a similar issue where the fan wouldn't register as rotating fast enough on the first "boot" but if the button was pressed again it would work (this was confirmed by manually spinning the cpu fan and it would boot first time).

Does that help any?

[stewie-Y]

I tried that stuff and it didn't work.

I had the idea, though, to replace the CMOS battery. As soon as I plugged the power cord into the PSU after replacing the battery, the green light on the front panel lit up and the CPU fan started spinning, but they both stopped after only a fraction of a second and the computer wouldn't power on. Unplugging and plugging the power cord after that hasn't had any effect.

Edit: I took the battery out and when I plugged in the power cord I got the same result as before (green lights, fan spins up, stops immediately). I noticed that if I unplug the computer and plug it in before the AUX power light goes off, it will have no response. But, if I unplug, wait for the AUX PWR light to go off, then plug it in, the green lights and fan come on then turn off immediately.

What could be causing this?