Ok, I am running 10.04LTS so this should be very similar for you.
I did have issues with monitors when I first started using 10.04 I beleive this is the method I used to cure it.
sudo apt-get remove fglrx
I couldn't enable desktop effects in compiz so i id this:
sudo apt-get install xserver-xorg-video-radeon
sudo gedit /etc/ld.so.conf.d/GL.conf
above the entry that is already there, but make sure there are still two lines in that file when you save it.
then issue this command
this redoes the loader cache.
and just to finish off run
sudo apt-get update
your graphics should all work now with no bits missing around the edges of the screen or weird stuff at boot time.
I just could not seem to have any success with the fglrx drivers but if the xorg drivers do not work for you then you can reverse the process and remove the xorg driver and re-install fglrx.
You can of course install these drivers via the synaptic package manager if you prefer.
Hope this is of some help in resolving the issue.