Is it happening whenever you try to render any 3D graphics? In other words do 3D games other than CSS and DoDS work fine? My graphics card shit the bed a couple years ago with somewhat similar symptoms. Everything worked fine for 2D but as soon as I tried to play any game using 3D, everything would freeze and I'd have to restart my PC. I ended up just downloading a basic 3D demo to test with and it would crash every time I started it. Replaced the graphics card and problem was solved. This was back when Nvidia was having solder problems with their GPUs...