I only ever had one library - and no, it wasn't on a usb drive, just the computer. The only thing I find on my backup is a calibre2 folder which appears to be a program update of Mar. 8, 2019 to 3.40.1. The only drives are the OS (WIN 10) and the backup drive (Seagate).
I'll keep playing around with it since, I apparently can't do more damage!
I do seem to still have all of my books available on the original sources.
I appreciate your help - at least I feel I'm eliminating the possibilities.