Hey guys. I had a question about testing hardware. For a good while now, I've had all my PC games crash the computer to reboot whenever I'll play them. I don't believe this is a driver or software issue, as I've reformated multiple times (over the course of almost 2 years now) to try and fix the issue without any success. I've ran memtest to check if my ram was good and I had no error. How do I go about checking other components?   
 
Note: My computer has never crashed while not running games. 
 
Here are my specs, although I'm not sure it is needed. P5B Deluxe Motherboard, Core 2 Duo 6400 @ 2.13, 2gb of DDR2 RAM, and a Radeon X1950X with 512 mb, and a 750 watt power supply. This computer was built in late 2006. I've only changed 1 thing, and that was a 7900GT NVidia card that failed. 

Alot of things could be crashing your pc :
* Bad Powersupply ... what kind of power supply unit are using ?
*GPU overheating ... 
*GPU memory corruption 
* CPU overheating 
*Bad Case of motherboard 

Here are few test i would recommend running :
 
Run Prime95, fully stress all cores of your CPU. Run Prime95. 
Run OCCT , it fully stress test your GPU. Run it for 30mins. http://www.ocbase.com/perestroika/index.php?Download
 
I would recommend you do a simple upgrade : 
Windows 7 
4GB DDR2 Ram
Get a ATI 4850 : http://www.newegg.com/Product/Product.aspx?Item=N82E16814150482

Thanks for the suggestions, working through them right now. How would I test if I have a bad PSU?

Thanks for the suggestions, working through them right now. How would I test if I have a bad PSU?