Ubuntu 16.04 Install: No login prompt, no nothing

I scrapped the Ubuntu 15.10 install and installed Ubuntu 16.04 instead. The installation process seemed to go okay. There were no waings or errors. However, when I boot the machine, it gets to the pinkish/purple-ish screen and that's it. No login prompt (though I did configure the install for automatic logins). No GNOME panels. Nothing. There's a mouse pointer, and I can move it around. If I discoect the etheet cable, it flashed "Discoected from the network" or something like that, but nothing else is happening.

UPDATE: Actually, it appears I'm logged into the Ubuntu machine, but there are no icons displayed and not GNOME panels. If I Right-Click with teh mouse, I get the usual menu for creating Folders, or documents, or launching terminals, but that menu is flashing on and off about once per second.

If I create a folder, then that folder icon appears on the desktop, but it is flashing on and off about once per second

What is going on? The PC is an Intel I7 6800K, and the video card is Nvidia GTX 970.

What next?