Caot login to GUI with fresh 16.04 install

I just completed an install of 16.04 on a new system without any problems, but when the system (not the live USB) started, I get the (GUI) login screen, I can enter my password, then... nothing. Well, almost nothing. Only the background image shows (the text at the bottom left showing the Ubuntu version vanishes). The mouse still works, and I can Ctrl+Alt+F1 into a text login (and I can login there successfully).

I did see some flashes of stuff happening. In the top right I saw flashes of what looked like notifications about updates available. Then I saw what looked like an "Ubuntu has experienced an error" messages jumping between the top left and bottom right.

Could this be a graphics card issue? The card is an EVGA GeForce GTX 960.