PC shuts off when playing (some) games?

Hey all.

I'm having quite a weird problem. When playing some games (Oblivion, Guild Wars, The Frozen Throne), my computer will shut down after about 20 minutes off play time. My temperatures are all fine (CPU never hits over 50C when gaming...GPU never over 60). The weird thing is, it only shuts down during those three games. I can play Crysis and benchmark with Prime95 and 3Dmark without having this problem. It's really weird...do you think it could be the power supply? (I dont think thats possible because like I said P95 runs fine...and thats much more intensive). Conflicting drivers? Has anyone else had a problem like this before? I'm stumped.

Here's my specs:
Motherboard: MSI P7N Platinum 750i
Processor: Intel Q6600@2.4ghz
CPU cooler: Arctic 7 Cooler Freezer Pro
Graphics cards: 2x XFX 9600GT\'s in SLI
Memory: 4GB of OCZ Platinum DDR2 1066
Hard Drive: 2X 160GB 7200RPM Seagate Barracuda
Power Supply: Antec NeoPower 550W
Case: NZXT Apollo
Mouse: Razer Diamondback
Keyboard: Razer Acrosta
Monitor: Dell 2408WFP
Speakers: Bose Companion 5
OS: Vista Premium 64/Ubuntu 8.10

All help is appreciated.
Kind regards, your friendly neighborhood troll.

I would say that power supply is the most likely problem however 550w should be enough for your system. Have you ran memtest to check the stability of your ram, you could also try running with only one stick of ram to see if it makes any difference.

That is all I can think of if temps are fine, mabye someone else has any ideas?

Another small tidbit...the PC doesn't turn off. The monitor just goes blank and the computer is completely unresponsive.

I would remove the overclocking and set the voltage on the memory to specified specs. Then test to see if the system stays stable. If you still have issues remove one of the video cards and try that, may not have enough power for both.

I had a similar problem recently with my computer locking up & rebooting after 15mins only when playing GRID (UT3 was fine). I just upgraded from 2GB to 4GB and thought that might have something to do with it, but I tracked the problem down to the CPU VCore setting. It would appear that after running OC'd for a year now that my processor needs slightly more voltage. It's an E2160 @ 3.0GHz...original VCore was at 1.425 and I had to bump it up to 1.4375. I can't say for sure it's CPU wear, as I hadn't played any games for quite awhile, but it does look that way.

Orion, your the man!

I gave my CPU a little more juice and that fixed the problem. Thanks!