Problem with my comupter

I recently bought a new computer:

Processor: Intel Core2 Quad Q9400 2.66 GHz + Asus Lion Square cooler
Motherboard: Asus P5Q-E
Video card: SAPPHIRE HD 4870 X2, 2GB GDDR5
Memory: Kingston Hyperx DDR2 2x2GB 800MHz
Power supply: Power LC1050 1000W
Hard drive: Seagate 500GB, 7200rpm, 32MB, NCQ, SATAII

Operating system: Windows Vista 32 bit / Windows XP / Windows 7 32bit
Drivers for graphic: ATI Catalyst 9.3
Monitor: Samsung 24 " + Samsung 19"

The computer works great in all Windows, only when I starts a game computer crash.
I can play for 5-20 minutes and then the computer crash again, only exception is crysis and I can play on 1920x1200 and all video setting on full.

The problem definitely is not overheating, because the processor temperature is 45, and graphic 70-75.
I know that they were some problems with the drivers.

So I try 8.11, 8.2, 9.1, 9.2 ,9.3 and the problem is still the same.

Computer isn't overclocked, so now i don't know what to do?