Solved the problem, in a way. Evidently, in my case, once I did a free upgrade and then uninstalled it, I was unable to do a free upgrade on that particular HD.
What I did, was to connect a second HD on which I had cloned an early version of Win 7. Ran a clean install on that drive, the updates took a while, then I was able to go back to a previous site and download a free Win10 upgrade.
Took some time, but it worked. Thanks also for your help.