I was having trouble getting a Dx8 game to run. It said it couldn't use Direct3D, even though MM9 was running fine. I went to the DX Diagnostics and tested D3D and got an error.Now, on the same page there is a button to enable or disable D3D. It read 'Disable' at the time. I clicked it and got the message that D3D had been enabled. The label on the button didn't change. Hmmm. I clicked it again and was told D3D had been disabled. The button label changed as expected and it has been working properly since.
And that game will now run.