CPU/Mobo Mobo only powers up without the 4 pin cpu power plugged in

[sumchamp]

With only CPU, Speaker, PSU, and Mobo plugged in, everything powered on for a split second and then powered off. However, if I disconnected the 4-pin power supply to the motherboard, the computer will turn on and stay on (of course it doesn't boot, but it stays powered on...). If the 4-pin power is connected, then I get the turn-on-turn-off effect.

Which could be the culprit, mobo, CPU or PSU?

Specs-

Mobo : ASUS M4A78-EM/1394
PSU : CORSAIR HX650
RAM : 2x2GB OCZ

 

[vivek.krishnan]

I have a feeling its the board - remember reading a similar issue elsewhere. Would suggest to check if the PSU is faulty as well.