Well, so far, this topic hasn't generated much interest. I have an update:
I fresh installed Windows and copied my Opera files to the proper location and everything was fine for a few days. Today, Opera wouldn't start again. I thought the fact that on the previous Windows installation, I was using a local account rather than the Microsoft account I was required to setup might have been a cause but since I did the fresh installation, I have only used my Microsoft account.
It looks like one step forward and another one back!