I just tracked down a 3d rendering issue to some free virus scan software that Bonk and I recommended here a while back. It would seem, but I am not totally, absolutely, 100% sure that this free software blocks Directx3d rendering. I haven't been able to independently verify this so if anyone who has also downloaded this freesoft would not mind, could you run your dxdiag and run the Directx3D rendering test?
Lemme know what you find.