Computer randomly shuts down during games!!

[bigdogsleeping]

Hey guys, Ive been trying to fix this problem for a few days now. I just built a new computer and when ever I play games it will just randomly shutdown every once in a while. Heres all the things I've already tried:
I've tried reinstalling every driver imaginable.
I've monitored the CPU temps and they never go above 50.
I've tryed different sound and graphics cards and it still happens
I've downloaded windows updates
I've run virus scans.
I've made sure nothing is shorting out in my case.
I've run every part of tuneup utilities 2006.
I've tried just about all the setting in my bios, I don't overclock.
I used the RAM, sound card, and video card in my other computer and had no problems.
I did a repair install on windows.
I ran a diognostics on my harddrive. Every things fine.

Ive tried all these things and my copmuter still just shuts down in games. the only thing I could think of is maybe somethings defective. I don't know, I'm getting really desparate. PLEASE HELP ME OUT!!!

Here are my full specs:
Amd x2 4200+
asus a8n sli
evga 7800gt
cooler master wave master.
sony dual layer dvd drive
Antec neo HE 550 power supply
pqi dual channel ddr400 RAM
74gb western digital raptor HDD
Creative X-fi sound card xtrememusic

 

[pscowboy]

You've covered a lot of troubleshooting. I have just one suggestion. Random shutdowns are sometimes caused by cpu overheating.

Double check the relationship between the cpu, heat transfer layer (pad, or paste), and the sink (and its' clip).

 

[hao129]

Another thing that might cause random shutdowns are power supply issues.

 

[khha4113]

Are there compatibility issues between ASUS motherboards and Neo HE power supplies?


We have received multiple reports of such issues, and ASUS and Antec technical teams have been able to confirm the existence of a random problem. If you believe you have encountered this incompatibility, please do the following:
1. Update your motherboard BIOS to the latest version. This step solves the incompatibility problem in a majority of cases.
2. If you have successfully updated your BIOS and still encounter the compatibility issue, please contact Antec Customer Support for a replacement power supply unit that has implemented a fix for the "ASUS motherboard problem."