Halo Hardware Acceleration not enabled?

Every time I start the Halo demo I receive an error saying "There was a problem initalizing Direct3D, Hardware Acceleration may not be enaled. Run DXDIAG" Except DXDIAG says that Direct3D is already enabled so what is the problem?

Halo for pc is a picky piece of cr@p I've been fighting forever. Uninstall and reinstall the game. I've had the same error among others.

It was because I was using Reforce, I disabled it and it worked fine.