On the bad cable theory, this is not clear, since I tested with more than one, and I used my FTDI adapter to separate the power-only/charging cables from those that have active data lines (D+/D-). Under Windows 10 I assume that if I get a beep when I connect the FTDI device then the data lines are active. Otherwise, I assume that the cable is power-only, and do not use it for testing my Arduino Nano. After filtering out the power-only cables using this test, all of my mini USB cables do not work with the Arduino Nano, while all of my micro USB cables (+ micro/mini adapter plug) do work. What is really strange about this is that at some point in the past the mini USB cables did work! [One of my theories is that a bad cable may have damaged all of my Arduino Nano's, resulting in this odd behavior. If this is true, you are correct, and the source of the problem is a bad cable.]
Do you think my test for power-only/charging cables will always work? Do USB cable testers exist?