After upgrading from 16.10 to 17.04, I get through the grub menu, then get stuck at a black screen with 5 squares on it, each square with a dot that is either red or white. The page cycles through these dots, changing them from white to red, then back to white.
I can't find anything about this page anywhere on the internet, so I don't know what it's trying to convey to me.
I can ssh in over the network to this node, so the system is up, but it doesn't respond to mouse, keyboard - just cycles through the dots. Have looked at all the logs in /var/log but don't see anything odd. So no login screen, no desktop. I've included a picture.
I'm running an Nvidia graphics card. Haven't changed anything regarding that from when I upgraded from 16.10 to 17.04, and it worked on 16.10.