Random crashes in games.. Any ideas?

[Turiel]

Hello there... Lately i experience an issue with my computer when am playing almost any game (Need for speed the run,BF3,UT3,Fear3 etc)
my build crash without any reason I DON'T get any blue screen it just restart..
I make sure drivers are all update windows as well. I also run some stability test with Everest all fine and 3D mark 11 benchmark.
CPU temperatures all are good 40-idle and 55 in games (Celsius)
Wattmetter shows 170W idle and 262W max in games
I dont know what to do i tried a lot of things
*I dont have anything overclock

edit This is not happening always some time am playing fine for 3-4hours and some times after 20min MPAM Restart is just random

My build:

Motherboard = Asrock X58 extreme3
Cpu = intel i7 960 3.2Ghz
Ram = 6Gb Kingston HyperX DDR3 triple channel 1600mhz C7
Graphic card = Asus ATI HD6870
PSU = Thermaltake Toughpower 650W
HDD = Seagate Barracuda 1TB
Windows 7 professional 64Bit

Any help guys am gonna appreciated

 

[clutchc]

Have you tried cleaning your system of resource wasting garbage and registry errors? If not run CCleaner and do the Clean and Registry both. Defrag.
Have you installed many graphics driver versions over the time you had the system? If so, uninstall the existing driver, boot to Safe Mode and run Driver Sweeper to remove remnants of any old ATI, AMD, or even Nvidia video drivers it finds. Reboot and install the latest AMD graphics driver.

http://www.piriform.com/ccleaner
http://phyxion.net/item/driver-sweeper.html

 

[jsc]

If the system "randomly" resets/reboots during gaming but no other times, my first suspect would be the PSU.

 

[clutchc]

+1
Another good point.

 

[Turiel]

Thnx clutchc registry seems was the problem something with nvidia physx stuck there (dunno how they gets there) i never own nvidia card

Thanks all of you problem look like solved