I have not been able to try anything for the past few days.....I tried copying the file to the hard drive...no change. Chaley and cybmole, I'm afraid I don't understand what you're suggesting - it's way above my tech knowledge.
I did try starting with a fresh install of Calibre, and when the blank library came up, I connected the Kindle that has the most books on it and said to add books from the device. It seems to have done that, and I think I've got the plugboard set up properly. I can't figure out how to save the new library. I ejected the Kindle, and now I can see the list of books, but can't seem to get it to save the library.
Sorry to be so dense. . .