Computer instantly powers down during COD2

[LDRunner]

Finally have my system set up but it keeps instantly power down during COD2. This is similar to the problem I was having before I got the updated NeoHE 430, except now it only happens during 3D game play. No problems in Windows doing HDV capture and rendering. Is the PSU not powerful enough to power the video card in 3D mode? Any ideas on how to troubleshoot this without another PSU? Really regretting getting the Antec case now.

Forgot to mention that nothing is overclocked, except the 7800GT which comes overclocked from eVGA.

 

[mshan]

CPU Overheat protection? (is the whole system and everything connected to that psu shutting down all at once?)

Double check that your heat sink is seated correctly and you've applied a thin layer of appropriate thermal paste. Is there a fan on the Sythe Ninja and is it spinning?

 

[LDRunner]

Yeah, everything is shutting down at once. Heat sink should be fine and there is a thin layer of artic cerammique on there. There is a fan on the Ninja that is automatically controlled by the motherboard.

I initially thought it was a CPU overheat problem, but according to Asus PC Probe II my CPU temperature is higher when I am rendering HDV than when I am playing COD2.

 

[mshan]

I think cpu overheat protection would kick in when the thermal diode temp hits a preset limit (and this temp is not probably what you see in Asus probe, which is probably a socket sensor temperature, and even at that may not reflect the real temps in the cpu).

I would say take the cpu heatsink off and reseat it just to be safe (also, does the heatsink feel warm when you are using the computer and have you visually confirmed that the fan is spinning when you power up the computer?)

If you think COD2 is overloading the psu, maybe try turning off all of the eye candy and lower the screen resolution so that it's not so demanding and power drawing on your gpu and see if the sudden shutdowns disappear?

EDIT: other thing you could do is lay your computer on it's side so that the Sychte Ninja is "upright." If cpu and heat sink aren't in good contact (e.g. heat sink is sagging away from the cpu while in your vertically oriented mobo), it could be leading to less than optimal heat transfer. Solution would be again to remove the heat sink and reseat it.
Other thing to note is that Artic Silver Ceramique takes a little while to settle in, so it may be a day or two before it conducts heat away optimally.