Screen goes solid colour when gaming.

PROBLEM:

I've had my Alienware computer since about April this year and I've just ran into my first problem with it this week. I only play two games on it; World of Warcraft and Call of Duty: Modern Warfare 3. After about 30 minutes of gaming give or take my screen goes one solid colour and I cannot even ctrl+alt+del out. I have to turn off my computer by holding the power button down. When the screen is a solid colour you can hear the last bit of sound occurred before the error. So if it was a gun bullet it keeps on repeating that sound until the computer is shut off. All my drivers are up to date and my diagnostics all pass on the dell site.

SPECS:

Product: Aurora-R4

Processor: Intel 1.7 @ 3.2

Ram: 8GB

Video Card: GeForce GTX 560 Ti

If you need any additional information just let me know.