There might be a problem with upgrades. The best action would be to boot to the older system.
The first way of doing it while booting hold SHIFT
button till you see Grub menu. Select older version and press ENTER
, if you don't see older version select
Advanced options for Ubuntu
and press ENTER
, then select older versions.
After booting OS you can try to reinstall the upgrades. If not sure what to do edit grub.cfg and add the older version to the top.
If nothing works, connect to WiFi (description here).
Then reinstall latest upgrades and fix Ubuntu (description here)
If both does not work, try this help from ubuntuforums.
If that doesn’t work, backup user files and try clean install of latest Ubuntu. I would not do it, though.