it could also be your cpu ?virtual memory could be coming up short.. even a virus could do something like this.. perhaps it sounds like a problem with your video card to be honest.. direct draw or something, you might want to update your drivers or even downgrade them.. sometimes updates have problems.. i'm currently working through getting star wars galaxies to work and i know it worked on my original settings so a full system restore could help. try all or one of these at a time