I'm an absolute beginner with ubuntu. After installing 11.10 I get a message to install ATI proprietary driver. The new one can't be installed, the older one get installed. After installation I must reboot. I do so and my monitor shows me something like "70Hrz horizontal and 60Hrz vertical are not supported" on a black screen. I don't find a way to set other resolution like 1024x768 or 1280x1024 and I can't see something, even CPU seems to be working.
From the above forums post, boot to recovery mode and run the following commands
Reboot and X should work.
You can try to install the proprietary drivers, check to see if your card is supported first
Supported hardware : http://wiki.cchtml.com/index.php/Hardware
Installation guide : http://wiki.cchtml.com/index.php/Ubuntu_Oneiric_Installation_Guide
you might want to look at this-