Also, I upgraded to 18.04 in an attempt to get away from the problem - but that didn't work either (should've guessed...). BUT another problem emerged: when trying to check and install updates (I have 290+ updates to make) one of them apparently fails and the process stops without installing the other ones... have tried it 3 times now with the same result. The problem is this: "E: Failed to fetch https://netix.dl.sourceforge.net/project/ubuntuzilla/mozilla/apt/pool/main/s/seamonkey-mozilla-build... Undetermined Error [IP: 87.121.121.2 443] E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?"
Tried apt-get with no luck and do not understand what is meant by the --fix-missing approach...
Well, the changes for the hibernation and the lid changed the finishing lines of the shutdown process and the look of the screen after it was once again opened - but no change in the absolute outcome (still now powering off and still a frozen computer). I guess I will just have to power the computer off by pressing the power-button for 5 seconds or so and not to shut the lid.
Regarding the check and install updates problem, it was just me being an idiot and having seamonkey-session ongoing... everything is ok on that part.
Ok... sorry those solutions didn't work for you. I think I'm finally going to be making a change with seamonkey... it's getting harder and harder to keep it going. I seem to be constantly mending it.
I installed Vivaldi, runs a little too slow to be usable for everything on my system - but has the advantage of adding the chromecasting button for youtube compared to seamonkey.
In the highly unlikely event that anyone runs into the exact same problem as I did, I have found a solution: 1. In terminal write: sudo pluma /etc/modprobe.d/blacklist.conf 2. Scroll to the very end of the file and write: blacklist wistron_btns 3. save and close the file 4. Restart the computer (shutdown/reboot the old and non functional way) 5. Now the computer should poweroff as intended