Crashes in L4d/Crysis Warhead

Whenever I play Crysis Warhead or Left4Dead my computer will crash periodically(sometimes beginning after less than 20 minutes). By Crash, I mean that the screen will change to a solid color and the sound will screech, and the computer will remain in this state until I reboot it.

Also, the computer is 1 month old, and these problems started last week. I was able to play through all of crysis with out this issue.

My psu is often quite hot (~70C), so I monitored the voltages while I was playing warhead and noticed they would not go below 11.52V on +12V. Does this voltage drop vindicate the PSU or prove that its the issue? Any tips on how to diagnose the cause would be much appreciated.

Specs:
Roeswill 500W psu w/(31A on 2 +12V rails)
AMD Phenom II 940
XFX GTX 260 (factory overclocked)
8GB DDR2-1066
BIOSTAR TA790GX
Vista 64-bit

Right before the crash in Crysis:
GPU 75C
PSU 76C
CPU 55C

The system idles at:
GPU 47C
PSU 70C
CPU 40C

Also, the crash in crysis warhead comes soon after I start playing the first level in what appears to be a graphically intense moment. (I thought this was a problem with my install until I realized Left4Dead crashes the exact same way...but I could be wrong)

I will post temps while playing left4dead/extended high load when I get a chance.

I'm going to replace the PSU. Thanks for your help.