BSOD Memory Parity Error Running Windows 7

I own a Dell XPS M1710 running Windows7 (5 years old). The graphics card has already been replaced once (after 1 year) due to a well know heating problem (made tolerable by cooling pad). I get Blue screen and Memory Parity Error some of the times I start up but mostly it freezes at the black screen point. Memory check gives all clear and I have tried swapping out all of the RAM with (working) modules but still get the same error message. Tried updating the graphics driver, no change. Tried disabling the Graphics device in Device manager and this had a slightly different blue screen but the same basic result.I suspect the graphics card Nvidia Go 7950 GTX because the fault first happened while playing an MP4 file.