I am reasonably sure that I have diagnosed the problem that was preventing me from connecting to the ethernet.
After some extraordinarily brilliant and high-tech diagnostic procedures (I swapped cables and it started working again) I discovered this bit in the 50 foot cable that connects to my router. (see attached photo).
Apparently when I connected my UPS battery Monday afternoon I somehow pinched the cable between the table leg and the baseboard electric room heater.
So now, the question: Do you think this was really what caused my loss of internet connectivity, or should I look further?

ps: Is there any conceivable use for a
fifty-foot uhh, now a 41-foot plus an 8.5-foot ethernet cable, each with a connector on just one end?

pps: This couldn't be caused by looking at porn, could it?

tanstaafl.