Windows 7: BSOD win32k.sys, how to fix?

Im getting BSOD with win32k.sys
It doesn't appear any specific (<- did i spell it right? ) time, and never on safe mode. If i start my computer normally it takes a long time with a black screen before i get to the Welcome-screen. And when i get to my account the computer usually crashes with win32k.sys or PAGE_FAULT_IN_NONPAGED_AREA (or something like that).
I have done a quick check with my avast!, no results. Microsoft security essentials wont update, and when i do a complete check with avast! computer crashes after a while, even in safe mode! So it might be a virus too...
im running Windows 7 64bit

Please help, the computer was pretty expensive and its new i dont want to get rid of it