Only lo-res video

Just did the software upgrade to 5.4.0-51-generic x86_64, and now my monitor is stuck at 640x480 resolution, with no options in the dropdown menu to change it.

Help!!! Thanks.

I tested the computer and monitor with a live 20.04.1 LTS DVD, and no problems with the display. Is there any way to resolve this issue without a fresh install?