Computer turns on and off when trying to start up

Hello--


I just finished putting together my brother-in-law's new computer and everything seemed to be working like a charm. But he told me that it shut itself off after he had left it inactive during the night and when he tried to turn it back on, everything starts (fans and drives and mobo lights all come on like normal) for 2 seconds, then shut off. It then tries again on its own and shuts off again after 2 seconds. It repeats this until you kill power to the PSU.

But if I let it sit for a while unplugged from the wall, then try again, it boots up as normal.


I can't figure out what's going on.


So far, I've tried unplugging the PSU from the mobo and jumped pins 4 and 5 on the PSU's 24-pin connector, and as expected the fans and drives all came on. (I plan on trying this again after the computer's been running for a while).

I want to try to solve the problem ASAP so I can send any faulty parts back to Newegg before my refund period expires.


Specs:

Mobo: Gigabyte GA-EP45-UD3P
CPU: Intel Core 2 Duo E7400 2.8 GHz
PSU: Corsair CMPSU-650TX 650 Watt
RAM: 2 x 2G Crucial DDR2
Video Card: Sapphire Radeon 512MB HD4850
HDD: WD 320GB 7200

Thank you for any input you may have.

Thanks for the fast reply. My initial thought was PSU as well. I think I'll take the risk and try to send that back for another.

Thank you

Hmmm, interesting point. I'll check the BIOS before shipping the PSU.

It seems that if RAM lacking proper voltage was to blame I could possibly force the issue to arise by taxing the system a bit.


I've had great experiences with Crucial (been using 2 sticks in my own computer for over three years now) and Newegg reviews looked good. I hope crappy RAM is not to blame.

Thanks for the advice.