Thanks, guys. It is with all humility that I can report it is now fixed. I decided a microprocessor reset was my next step. I hated the thought of having to set everything up again, so took A BUNCH of pictures of my current settings to help me remember.
This is where the humility comes in. Before the reset, I decided to simply unplug the unit. I let it sit for a while, then plugged it back in. It worked. I can't tell you how many times I have told people to reboot before trying anything else. Physician, heal thyself.
Oh well. I'll blame it on old age.