Or your CPU has a heat problem. First thing I'd try is taking the cover off and feeling the heatsinks. If they're too hot to touch (and leave your finger on) then they're too hot to work properly. Second, I'd replace the video card. Looks a lot like video ram errors. and when you force a refresh, it overwrites those spots again, so the errors go away. The LAST thing I'd do is reinstall windoze.