I retried getting the ISO, and this time it worked, so I took a bet and upgraded in place, just completed 3 minutes ago
The first few things I ran seem to be OK, a few icons missing from the desktop (Excel files, for instance) but that is no big issue
I won't be able to check Windows Update tonight, but I expect the problems are history (temporarily at least)
I want to thank you for all you have done to try and help me.
Beyond the standard way of expressing my gratitude, I would be delighted to offer you what we call a "paiement en liquide" if you ever come to Belgium. Be sure to let me know.