Is my CPU or MOBO toast?

Last night my computer just shutdown for no reason. When I try to turn it back on, the fans light up for just a second but nothing more.

I turn the power off from the back and then once again, just a second of power and thats it.

I swapped power supplies, same thing. I unplugged all hardware, same thing. I took the CPU out and looked to see if it was burnt but it looks totally fine. Put the CPU back in, same blip for a second and thats it.

I have an ATHLON 64 3500 AND 939 pin Mobo.

I ronically, I tried putting together an old P4 that seems like it should be fine with a new MOBO and on an entirely new case, same exact problem as stated above.

Whats going on here guys?

 

Well I am not a 100% sure but it did the exact thing that my Demon PSU did.

The thermal grease looks great and everything and even if it got to hot, wouldnmt it just shut down and then let you boot back up again?

Should I take the CMOS battery out and try that or swap video cards?

 

Everything looks totally fine on the system. Who knows at this point but I wouldnt think the athlon 64 3500 would overheat once and thats it would it?

If it was my PSU, wouldnt it be gradual or smell of smoke etc..?

 

O.k., here is what I did. I took the Demon PSU 580watt and plugged it into the only computer running at this time, a Pentium3 1.0 ghrtz.

I plugged it into the MOBO of the P3 and the Demon PSU instantly fired up with the fan etc.. and then after 5 seconds stopped. I did not want to try it again.

Did it stop because its simply too much wattage for the P3? or did it stop because this is the actual culprit?