I just bought this kickass computer and now it won't even boot... it's been running fine for some time now, but when I got to my dorm this afternoon it was off (even though I leave it running 24/7)...

when I push the power button, the only thing that happens is the lights on the case fan go on, and then off again.. you have to be looking right at it, it happens so fast... not a sound from any fan trying to spin up or anything like that... also the lights on the fan only blink the first time you try to swith on.. after that you have to flip the switch on the ATX PSU of-on then you can do the fan-lights-blink again, once... weird...

all memory, devices are out of computer... it's just a mobo and CPU..

my only idea so far is that the PSU has gone bad.. it says 500W but it came with the case so I don't know if it's used or what it's story is... I have a multimeter.. can someone give me some ideas as to how to test the PSU? I don't know which wire pairs are supposed to have what voltage...
or if someone has a spare PSU they would be willing to let me borrow to test (any maybe even buy if that fixes it) that would be very much appreciated...

EDIT:
there is an LED on the mobo that is lit when the PSU is switched on so the mobo seems to be getting power.. but maybe not enough to boot?

Get a paper clip, and stick one end in the green wire of your 20-pin ATX connection. Stick the other end in any black wire. Then turn it on. That will allow the PSU to be turned on without it being plugged into the motherboard. If the PSU fan is running, then your PSU is alright, and your mobo is probably at fault.

yellow wire is supposed to be 12v +/- 5% under load
red wire is supposed to be 5v +/- %5 under load

when shorting the green wire to turn the psu on, even if the fan spins, listen for any unusual sounds....unusual being anything other than a fan spinning.

This is going to sound really wierd and stupid, but is the power button plugged into the mobo? It should be a little 2-pin wire that connects to the SE corner (maybe close to where the floppy drive plugs in). That happened to me over the summer and really pissed me off when i found out it was that simple.

thanks all for help... it was the PSU and I have a new one now from and all is well