I recently had a hard disk failure. After picking up a new hard disk, I installed a fresh copy of Ubuntu 21.04, restored all my data from backups, and everything was working well. After a reboot, my system booted into a 640x480 screen and I am unable to change it. Display settings says "Unknown display". I have a 4k TV I use as a monitor using the HDMI input. If I boot using a live USB the display is full resolution, so I know the hardware is good.

I've tried these commands:

sudo dpkg-reconfigure xserver-xorg
sudo X -configure

Neither makes a difference. What can I try? I've been using Ubuntu since 2006 but really know very little about X11.

Thanks for any help!

Rich