I have two computers. This post is about the 64 bit computer that I was able to upgrade from Xubuntu 15.10 to Xubuntu 16.04LTS.
Everything went well during the upgrade. Then when it finished it gave me a window asking to reboot. I rebooted. The computer did not react the way it normally does when it reboots. This time, the screen went black and the monitor said: 'no input' and it shut off. I waited several minutes and did nothing. At that point I thought the computer was off (but it wasn't) and so hit the power button. This did nothing because the computer was on, and I didn't hold the power button down so it didn't power off. I decided to leave it and came back in a half hour and lo and behold there was my Xubuntu screen and I could see it was the 16.04LTS because it gave me a new background screen. It also had the window up for either logging out, restarting, shutting down, suspending or canceling. I figured to be safe I'd restart right away. So I did and when I did, it went back into that black screen mode where the monitor shut down. This time I didn't touch it for ten minutes--still nothing. (And I would roll the mouse every once in a while to make sure it wasn't the power saver turning the screen black.) I came back in another half hour and it was the same screen that came back after the first half hour passed. (In other words, it was the 16.04LTS screen again.)
Now I tested all kinds of things--the computer works perfectly. However, when I go to turn the computer off (getting the window giving me the options to either log out, restart,shutdown, suspend or cancel) I noticed that when the cursor is not on the window, the cursor becomes a spinning wheel that never stops. When I put the cursor back on the window, the wheel disappears and the arrow returns (and all the above-mentioned buttons are fully functional). So now it appears that my computer works great but if I need to do a restart it will take a half hour or so for it to do so. I have not attempted a full shutdown (which is how I turn it off) yet (for fear of not being able to get back here) but I will attempt it as soon as I finish this post and report back (even if I have to use another computer). Thanks. (Sorry for the novel!)
P.S. In my search for a solution the best link I came across was the below one, but unfortunately it presented no clear-cut solution.
http://ubuntuforums.org/showthread.php?t=1469119