[newbie] Display problems

[Mark Lehman]

I've just installed Mandrake 7.0.  I have a Diamond Monstor Fusion video card (like a 3dfx voodoo banshee).  Everything was working fine as far as the display goes, but then something happened and every time I execute startx and go into gnome or kde, the screen is so dark that I have to turn my monitor brightness all the way up and I still can barely see anything.  Does anyone have any idea what I did wrong and how I would correct the problem?  Since Gnome and KDE displayed fine before this, I would assume it's not a problem with campatibility with my video card.   Mark