I began the upgrade from 10.04 to 12.04 in update manager. An hour or so later, after all downloads and about halfway through package installation, dpkg hung. It wouldn't respond to a kill -1 or -15, and I couldn't proceed with the graphical interface.

X wouldn't start after reboot, so I checked the upgrade instructions for a command-line interface. After 'apt-get install do-release-upgrade' and 'do-release upgrade', the upgrade appeared to proceed normally.

However, I cannot find a way to change the screen resolution. System Settings/Displays sees only display type Laptop, and gives me only 800x600 and 1024x768 as choices. That sux on a 23-inch monitor which had been doing 1920x1080 under 10.04.

Do I have to reinstall from scratch to get the display to be recognized, or can I fix it somehow?