I have been running Ubuntu 9.04 for some time. I changed displays on my PC to an
LG W2243T. My PC seems to have an ATI Radeon 2100 display adapter. Because I was
getting incorrect display utilization, I searched and found envyNG which
reputedly would install a recommended ATI driver for me. Now after restarting
Ubuntu, the display is totally unusable. A bunch of garbage is being displayed
and I can't get logged in.

When I run Ubuntu from the install disk in "trial" mode, I get a beautiful
display, which appears to be exactly what I want (16:9 display ratio), so Ubuntu
can detect my hardware and give me a correct driver. My question is: what can I
do to remove / replace the driver on my hard drive to get this same level of
display and recover my system and its installed products and files without
having to totally reinstall Ubuntu?

I tried the rescue option, but came out with the same situation when I was given
the choice of rebooting later in the rescue scenario.

Is there anything I can do or do I have to start over with a clean hard drive
and a total Ubuntu installation?