Asus m4a79t deluxe will randomly not post

I recently built a computer for a friend with an asus m4a79t deluxe mobo. It has a weird problem where it occasionally will not post at all. After resetting the cmos about a dozen times, removing the button battery, etc. it finally came back and we got windows installed and running. Everything was fine until this morning when it won't post again.

I don't understand it, why would it work perfectly one day and die the next?

I figure it's the power supply, because resetting the cmos doesn't seem to have any effect. It will just randomly start working again.

What do you guys think?

Specs:
Asus m4a79t deluxe
AMD Phenom II 955
Gskill ddr3 1333 4 x 2gb sticks
EVGA 9600gt
Corsair 650watt psu (cmpsu-650tx)
2 x western digital 1tb drives in raid 1 config