Lost video playback

[Blind Tiger]

After a clean install of Ubuntu Hardy Heron, and a complete install of VLC, my DVD playback quality was poor -- including stutters and poor resolution, especially at full screen.

I then installed the latest ATI driver for my X800 GTO using EnvyNG and found that I've lost video playback with VLC. It flashes the video output for a split second, then goes blank, and I continue to hear the audio output. I've purged and reinstalled VLC with all required dependencies for DVD playback, but have not regained video output.

How can I restore video output?