So I just bought a Radeon 4850 for Directx 10. I was using a Radeon X1900. I uninstalled it, cleared registries, etc etc. Popped the new card in and installed the drivers from the box. Everything's good so far. But when I reboot the computer and the card is ready for use, windows still says my X1900 is still in place. It's pretty weird. Device manager says my 4850 is in, but DXDiag says my X1900 is there. Directx10 won't load because of it.

Any ideas?

quite random indeed, have you tried reinstalling dx10?