What is your video card??
Is it in the "Known Working" list below ??
# ATI: Radeon 7000 through X850 (r100 through r400 generations).
# Intel: i830 through i945. i810 works, but DRI requires 16 bit depth.
# nVidia: all cards supported by the driver 1.0-9625 or higher.
# Matrox: MGA G550 works with current proprietary matrox driver for Xorg 7.0 or unofficial driver from http://matrox.tuxx-home.at
for Xorg 7.1.