Computer will not turn on, please help

Problem: I push the power button and the fans and lights turn on for about half a second then everything shuts off. The computer turns on and works for about 10 min about 1 out of every 100 tries. The computer has worked fine for the past month and a half. The only changes have been windows automatic updates.

The lights on the motherboard remain lit.

Specs:

G.Skill ram 2x2GB PC-6400 (DDR2 800)
Intel Q9550 - stock speed (2.83Ghz) (aftermarket cooler)
Western Digital 7200 RPM 320GB HDD
2x Asus 4850 Radeons (crossfire)
DFI Lanparty DK X38-T2RB
Windows Vista 64-bit
ZeroDBA 620W PSU
DVD-RW drive

I have tried just one ram stick at a time and just one graphics card at a time. No luck.

Any help would be appreciated.

Thanks.

The ZeroDBA 620W is sold by AeroCool.