Comment 12 for bug 133214

The support for these cards is pretty recent, especially when it comes to DRI. See also https://bugs.freedesktop.org/show_bug.cgi?id=6149

For tribe 5, boot in "failsafe" (vesa) mode if that works, and please test the newer xserver and xserver-xorg-video-ati from http://users.tkk.fi/~tjaalton/dpkg/ . Remember to switch back to "ati" driver after installing these packages. "sudo dpkg-reconfigure xserver-xorg -phigh" will give you a menu choice where you select ati, or use the new graphics driver selection in System->Administration (although I am not sure how reliable that one is). It would be very good if you can provide a Xorg.0.log from using the newest versions.

See also https://wiki.ubuntu.com/XorgOnTheEdge for more on testing versions.