You may have fixed this by now, but here is what you may have to do to fix this:
1. login as root in console mode
2. check to see if the radeon module is loaded (lsmod)
3. a. if it is not loaded try loading it (modprobe radeon?)
b. if it is loaded check your XFree86-4 file (probably in /etc/X11) and look for the graphics card section (it should be marked as the device section) see what driver the configuration program choose for you (probably either "radeon" or "ati")
4. if it choose "radeon" try "ati" or vice versa and then try "vesa"
5. if none of this works try getting the proprietary drivers from ati's website
http://www.ati.com/support/drivers/l...=11&submit.y=5
follow the directions on their site to set up the fglrx drivers (this is what I had to do on my debian box for a 9600SE card, with a 2.4.25 stock kernel)
NOTE: that this may or may not fix your problem (you may just have screen resolutions or hsync/vsync values that are wrong for you monitor)
see
www.xfree86.org (particularly
www.xfree86.org/help.html) for more info BEFORE attempting steps 3-5