i have seen a thread somewhere (sorry, can't remember the link), where people have had problems with the framebuffer device and the video card bios.
If you're running 9.1, i would strongly suggest that it is their kernel that is hosing things up. I installed a new ti 4600, and tried to boot to my old 9.0 and got nothing but kernel panics, and blackness.
Anyway, I'm on gentoo now, and it runs (so far), like a champion. Have not yet been able to do X (it's still compiling).
You could try this, at a mandrake boot prompt:
perhaps that might help