Computer powers off without warning

Just finished a new build to get back into gaming after a four year hiatus and have run into a problem. System runs fine during Win7 operation and with light tasks(ie: playing movies, music, etc.). Problem occurred after I installed BF2 and started playing. About 25 to 40 minutes into game the computer loses power, as if you flipped the switch off on the power strip. System will not power back on until i flip master power on back of PSU to OFF and back ON. All the components are new so dust or age is not an issue. I have also double and triple checked all connections; all secure. Nothing in system is OC'd, all running at factory speeds. I suspect it to be an issue with CPU temp, Graphics card temp, or underpowered PSU. Any help would be greatly appreciated. Specs follow...

AMD Phenom II X4 965 Black CPU w/stock heatsink & fan
MSI 790FX-GD70 Mobo
4GB OCZ AMD Black Edition RAM
XFX HD5850 1GB Black Edition
LG 8x BluRay
WD 1TB Caviar Black
Ultra X3 1000 Watt PSU
Cooler Master Storm Scout tower
Win7 Pro 64bit

 

I would check all the temps. I use SpeedFan for temps.

The you having to turn the power on and off on the psu makes me think it's a short.

It could also be a bad PSU.