Fw: problem with Mpact graphics card on Windows 95

Hi all,

I am writing a game using SDL on Windows 9x/ME/2000 which appears to be
working on most computers we have tested on - except my own at home! The
display is not working.

The one at home is running Windows 95 and DirectX 5 or 6, and has an old
Chromatic Research Inc. Mpact graphics card with a claimed 3Dfx chip
onboard. I initialise the SDL video subsystem, then open up my
screenmode with the following syntax:

screen = SDL_SetVideoMode( 800, 600, 16, SDL_HWSURFACE | SDL_FULLSCREEN

The screen will be persistently black, but the game will be running in
the background. When I manage to exit the game and start it again, the
screen will flicker once, then exit as if it is unable to open the
screenmode. All other programs on the computer behave normally before
and after this attempt, and I have been running a number of games,
including Jedi Knight and Mysteries of the Syth on the computer without
any trouble at all.

Any obvious or less obvious reasons why this should be happening?

Thanks in advance