Success!
After successfully installing a Calibre plugin, suggested by PeterT, Calibre could 'see' the Libra.
Peter's comments about the screen made me wonder if I was ejecting the ereader correctly, so instead of ejecting using the 'hardward eject' icon in the taskbar, I went to My Computer, Kobo, right-clicked this, then chose Eject. I saw what Peter described: a brief progress bar as the Libra switched itself on and displayed ALL THE BOOKS I'VE PUT ON TODAY er . . yesterday.
Thank you so much to everyone for being so patient. I hope this thread will help others migrating from kindle to kobo.
