PC reboots with blue screen

[Elsie]

My config:

Processor: AMD Phenom 9950 Quad-Core.
Graphics: ATI Technologies Inc RV770 [Radeon HD 4870] (1GB).
Motherboard: Gigabyte GA-MA790FX-DS5.
RAM: Gskill 1066 MHz 2GB of RAM.
Power: Cooler Master Real Power M620 600W
Hard drive (may be irrelevant): Samsung 500GB.

So here's my problem: when I start the PC all goes well I run the steam to play CS 1.6; msn to play msn music etc. But when I run, another example, games like Far Cry 2, Cod 4, Cod 5, PES 2008, Crysis, Grand Theft Auto IV to launch the games, the pc reboots immediately. Also once I got a blue screen telling me to change something in the BIOS.

I think my graphics card, also tested processor and motherboard on another PC and everything works well. I think it may be the problem of overheating because my processor is at 46 °C, graphics card 50 °C and my motherboard is at 29 °C as specified while playing cs 1.6 whole day.

[Alexisus]

Try to run a test with OCCT for several hours to see if the problem is of hardware or software.

[Elsie]

I have already tried it but it reboots my computer after every 5 mins of test.

[Alexisus]

Then surely a RAM problem, have you tested your RAM? Just use memtest86. If you have an error(s), either your RAM chips are bad or they are poorly paid at timings or voltage in the bios.

[yosoft]

Its not a problem with the Ram or anything it is a problem with your ATI graphics card. Try disconnecting it and try to use the integrated one. Check whether that works!!

[Elsie]

Its not a problem with the Ram or anything it is a problem with your ATI graphics card. Try disconnecting it and try to use the integrated one. Check whether that works!!

If it is the problem of my graphics card then how can I play CS 1.6 on this computer without any such issues. Why is this happening only with other games and not with CS 1.6? Can you explain me in detail?