I often get trapped when I don't follow advice of "Never upgrade Ubuntu"!
In procedural way, (attempted) upgraded from 14.04 to 16.04. Though I got some errors in the end stating something like:
Your upgrade was finished but had some errors.
After that my PC was neither restarting not shutting down. Hence I had to hard press the shutdown. Now I am writing this question from mobile, because 16.04 has never started! :-(
The boot menu appears & upon selecting the regular Ubuntu, it freezes after a while to a blank screen which shows:
/dev/sda5: clean (some blocks)
The login prompt never comes. I ran various options from "recovery mode" including fsck to no help.
If I get to 16.04 then better, but will be happy if I get my 2 hours prior 14.04 as well.