First, look for a file in /etc/X11/ that's XF86Config-4.old. If you have that there, either su if you're in a user, or login as root. Then do:
cd /etc/X11
cp XF86Config-4 XF86Config-4.old2
cp XF86Config-4.old XF86Config
When it asks if you want to overwrite the file, say yes. Then reboot. That SHOULDd restore the install to the original config file if you used the ATI drivers to make the new one, etc.
If that isn't possible, you'll have to use vim or emacs to edit your XF86Config-4 file. I use vim because someone taught me how, emacs may be easier.
First, log in as root or su, then type
vim /etc/X11/XF86Config-4
The interesting part about vim is you have to use weird key combinations to do anything. But first we want to find your Section "Screen", Section "Monitor" and Section "Device" settings for the graphics.
In vim, you have to hit the INSERT key to type things into the file. When you're done modifying, hit the ESC key. Then just type :w to save it, and :qa! to exit vim. If it shows the :w in the file and not at the bottom of the screen, you haven't hit ESC hard enough.
Basically you need to make sure that all the device names match up. For instance, you could have Identifier "device1" in the Device section, Identifier "monitor1" in the Monitor section, and then you must have Identifier "screen1", Device "device1", Monitor "monitor1" in the Screen section.
Find your ServerLayout section and make sure it says Screen "screen1" (or whatever your identifier for the Screen section is.
If that made any sense, and doesn't work, you're beyond my limited knowledge.
You probably want Driver "vesa" in the Device section too. Not sure if the radeon driver exists in M9.0.
Good luck.
(and thanks to anyone who corrects all my probable errors in this).