So I installed Calibre -- the epub reader -- on my Xenial drive and noticed right away that the icons on my top-panel & my desktop were suddenly all-white with a red "X" on them.
I re-booted, and the login screen was black (background image totally not there), but the username & password boxes still appeared, so at least I could log in.
The second I was logged in, although I could see that my startup programs had loaded, instantly the entire screen on both my monitors did this whole BLINK-BLINK-BLINK-BLINK thing and just kept up like that. So I can't use my 16.04 system and am posting this from my 14.04 drive.
I installed Calibre according to the instructions on its download page here. The command used was this:
sudo -v && wget -nv -O- https://raw.githubusercontent.com/kovidgoyal/calibre/master/setup/linux-installer.py | sudo python -c "import sys; main=lambda:sys.stderr.write('Download failed\n'); exec(sys.stdin.read()); main()"
I later removed Calibre with the recommended "sudo calibre-uninstall" but of course the desktop was, and is, still broken.
On the download page, below the install command, it says:
"You must have xdg-utils, wget and python ≥ 2.6 installed on your system before running the installer."
Since I have python 3.5 installed (and xdg-utls and wget), I didn't anticipate a problem.
Can anyone suggest what steps I might take to recover a functioning desktop in this situation?
Minor update: What's going on is strobe-light style flickering, but I've discovered I can actually enter commands between the flickers. Also, there are held broken packages, and I have to figure out how to deal with those. Re-installation of my Ubuntu-Mate 16.04 just isn't an option, except as an absolute final completely last-ditch effort.