I would guess that it is either getting too hot inside your case or you have a faulty stick of ram or it could just be a faulty install but i dont believe it is that.
Have you checked the temperature when playing the game, temp of cpu and gpu?
Is the inside of your computer clean? no dust on the fans ect?
*
http://www.cpuid.com/hwmonitor.phpThis is hardware monitor, free toll that will allow you to check the temps of your machine while gaming.
Have you ran a memory test on the ram at all?
http://oca.microsoft.com/en/windiag.asphere is the microsoft diagnostics tool and guide for the ram, you just burn it to a cd.
Let me know how you get on