I've a System76 laptop designed for Linux. I had it on Ubuntu 14.04, and wanted to upgrade to 16.04. I updated everything with apt-get upgrade then told it in the software updater tool to notify me about version upgrades. Even though I was expecting it to upgrade to 16.04, it only upgraded to 15.10 for some reason. After it was (supposedly) all done, I rebooted. Now, when I boot, it hangs indefinitely at "Started Update UTMP about System Runlevel Changes." I can switch and login with another terminal, and from here I can use sudo lightdm restart to enter the Ubuntu GUI. When I log in from here, the screen flashes a few times, then comes back immediately to the login screen. What is also weird is that the splash screen when Ubuntu boots shows Ubuntu 15.10, but here the login screen says 14.04 lts.
I suppose the problem is in something with the graphics, but have no certain idea about what the problem may be or how to diagnose it. I have tried to connect to the wireless while in the console, with the idea that I could try an update, but iwlist scan just says there's no scan results (even though this is incorrect).
When I look in ~/.xsession-errors, I see this:
Warning: only changing the first 21 of 12 buttons
Failed to get D-Bus connection: No such file or directory
xlib: extension "GLX" missing on display ":0"
INFO: imwheel started (pid=1802)
Script for ibus started at run_im
Script for auto started at run_im
Script for default started at run_im
init: unrecognized option '--user'
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 14 requests (10 known processed) with 0 events remaining.
I've seen both these behaviors (the hang then login loop) reported, but mostly with much older versions of Ubuntu, and the fixes documented haven't helped me so far.
How can I get this PC back usable?
