after few minutes of playing call of duty mw3 or black ops or any other game , the whole computer freezes and a black screen appears , at the first place i thought it was heat problem but the Graphics card temperature is like 60c and the cpu is 40c.
Processor : Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz 3.70GHz
RAM : 8.00 GB
Windows 7 64-bit
Graphics card : NVIDIA GeForce GTX 570
assuming your power supply is not the issue ,then gtx 570 is.
I'd first check for new drivers and then
re-seat the gtx 570