How do I know if it's the PSU?

I have a completely dead computer. I suspect it's the power supply, however I get one little bitty green light come on inside the computer on the mother board when I turn it on--absolutely no other response--except when I turn the computer on after it has sat for a while, the power supply fan will give a slow quarter-spin or so, then stop. So, the question is, what else could cause this complete lack of response?
Keith

 

Could also be the motherboard. Can you try another PSU in the computer?

It'll most likely be PSU or motherboard.

 

Well, I tested the PSU using the paper clip trick, and the fan spun and the molex plugs read 11.56 and 4.95 respectively. There's nothing else it can be but the MoBo?
Keith

 

The only way to be sure is to unplug or remove everything from the PC except the RAM. Try a boot. Does it POST ie beep to complain bits are missing? If yes start adding the the bits back one at a time with a boot each time to see if it beeps at you. When it stops beeping the last item you put back is the likely culprit.

If it doesn't POST with everything out and you've tested all the PSU outputs then it's the mobo.

 

Well, I tested the power supply on another computer. Granted it was an older computer and doesn't use as much power as the newer one, but it booted and ran fine. I don't think it's the PSU. So I got a new motherboard. I put the CPU, CPU heatsink/cooling fan, and RAM on it. It still doesn't boot, but now the PSU fan spins, the CPU fan and the case fan sorta spin. They surge. The pushbutton start light surges (bright, dull, bright, dull) in sync with the fan surge. The computer still doesn't boot or give any POST beeps or any kind of image on the screen. The only things the two MoBos have in common are the PSU, the CPU and the RAM. If it's not the PSU, I would think the CMOS BIOS would try to boot the computer and I'd at least get error messages on the screen... or beeps anyway. Still dead in the water.
Keith

 

What mobo did you get? If it requires more than one plug from the PSU you can get a surge with no boot. Post up the specs of what you have.

E

 

I got an Intel D865GVHZL. The power supply is a Bestec ATX-250-12E.
Keith

 

Re: How do I know if it's the PSU? (fixed)

Well, I replaced the power supply and the combination of power supply and new motherboard worked. I tried the new power supply on the old mother board and it booted up to the XP screen, but then would cycle off and back on again, so I just put the new motherboard back in. My guess is that the computer must have taken some kind of electronic surge to damage the power supply and the motherboard. Anyway, the hardware side is fixed. Not the software side though. I'm posting to software....
Keith