Surfaces/parts disappearing

Hi,

I don't know if this is the place to post this but i'll ask anyways.

I made an assembly with various parts for my third year project at university. Last Friday it working just fine but then on Monday as I moved the pointer around screen parts start to disappear. Clicking anywhere on the screen brings everything back but it is quite hard to actually do anything as random parts disappear. I tried restarting the computer and reinstalling the SolidWorks but has made no difference. The only thing I have done between these two days was some tutorials (3D sketching).

I'm using solidworks 2009 running on 64 bit Windows 7 if that helps.

Thanks

Alberto

SolidworksParts And Features