I've been working on a Voodoo1 system recently, and one of my cards seem to be having rather unusual problem... It doesn't want to work in DirectX mode, only Glide. Technically, it does load DX, but all I see is blank screen, the game still works in the background! I'm guessing that the signal doesn't make it to VGA output for some reason, as monitor goes to power-saving mode.

Does anyone know what could be the cause of this problem? And no, it's not software related, I've tried swapping cards... Glide on the other hand works perfectly, therefore I know it's not the GPU or memory bank(s). Card is Diamond Monster 3D, 4mb