[Omega]

Well, it's likely you've already thought of this, but was there anything you did shortly before you noticed the problem (ex. new drivers, delete files, un/install programs, etc.)? Also, make sure you have the latest drivers for your video card. It probably wouldn't hurt to remove your video card from the device manager, and completely reinstall it upon reboot.

Have you isolated it to D3D applications only, or all 3d applications? Try running the direct x diagnostic program (Start -> Run -> dxdiag) and testing direct draw and direct 3d and such. Then, try enabling or disabling those options like texture acceleration, or whatever.