There seem to be could be unsettled issues with this card.
1) in the Graphics device section of /etc/X11/xorg.conf, replace 'Driver "vesa"' (or whatever you have) by 'Driver "radeon"' (omit the single quotes)
2) chek that the radeon module is loaded: 'lsmod|grep radeon'. If not, load it. As root: 'modprobe radeon'
3) restart X
If that works:
- to tune your card's configuration, see 'man radeon'
- if it was not loaded, ensure that the radeon module be loaded at next startup. For that you can add following line:
to /etc/rc.d/rc.modules (more accurately, to the file to which the former links)
I cross my fingers