When my desktop rebooted after upgrading Ubuntu Gnome 15.10 to 16.04, startup gets stuck in a state where it constantly switches between a terminal and graphics mode, as if it tries to start graphics but fails. It keeps doing that every 10 seconds or so.
My system is a recent PC desktop with a decent NVidia GeForce GTX 970.
So I suspect a problem with the graphics drivers, and I'm savvy enough to try and repair it from a console... IF the system would let me have a console.
When I CTRL-ALT-F1 for the TTY1 console, I'm lucky if I can squeeze in a couple of keystrokes before it switches back to graphics (which doesn't work). Then I need to hit CTRL-ALT-F1 again to try and get the next few keystrokes in. This is not workable.
So then I decided to restart in repair mode. Same problem: can't get a working console.
So then I decided to try and repair it using the live DVD. But when I boot it it gets stuck. I get passed the UEFI stuff. I tried both "Install ubuntu..." and "Try without installing...", but in both cases startup just get stuck after a couple of minutes DVD activity.
Inspired by https://help.ubuntu.com/community/BootFromCD and https://help.ubuntu.com/community/BootOptions, I tried with several combinations of boot parameters, such as vga=791, noapic, noacpi, ... But none seem to make any kind of difference.
I've been using Ubuntu since Hardy, and I've hit "system broken after upgrade" problems several times before, but in all cases I was able to fix them using a console and/or live DVD. Except this time...
So I'm basically dead in the water here.