Everything tested, minus the display, seemed to work fine.

Nvidia drivers really, really didn't like the monitor I was using. The screen resolution would not fill the monitor area.
When I installed Xfce for a lighter desktop, for some reason I couldn't log out. This problem has since disappeared after a hardware change, with no explanation.

Granted, this issue is more related to the graphics card. (And will get moved, once I fire up the machine again and identify the card.)

I replaced the Dell monitor I was using with a Gateway monitor for using the Dell monitor to improve a different desktop, and the swap seemed good for both computers. The Nvidia drivers are kinder to this monitor.