A system which had been working fine wouldn't boot yesterday. It did not even POST, the fans whirred slightly & then just stopped. The system had a 500W ATX power supply. Of course I suspected the power supply & tried a 250W ps that i had in another system. It booted just fine w/ this ps. We purchased a new 500W ps & installed it. Nothing, same as the original problem. So I tested this new ps on another system & it booted right up. Put the 250W back on the problem machine & once again it booted up without a problem. I also had a 450W ps in another system so I tried that one & it too booted up. So I installed it into the case, turned it on & once again, I got nothing, No POST & fans start up & stop. This is the same power supply that booted up just a few minutes before. So once again I reinstalled the 250W ps and it booted right up.
Needless to say, I am completely baffled. Why does the 250W ps work every time, the 450W worked before it was installed in the machine & the 500W doesn't boot up the system at all?
Any suggestions would be greatly appreciated! If more details about the system are needed, I can supply those too.