Several messages fly by, the screen flickers a few times, then I'm presented with this the message mountall: disconnected from plymouth.
I've followed various threads that have similar errors. I've attempted the solutions in those threads, to no avail.
After the above message is displayed I can't type at the keyboard to log in. I've managed that machine in the past from SSH so I tried to SSH into it. That allows me access to the box and it's how I tried those other thread's attempted solutions.
I reinstalled the video drivers which had caused similar errors on several of my other Ubuntu boxes in the past.
Of all the releases of Ubuntu, so far, this one has been the worst when it comes to upgrades.