Whew! I was quite relieved and very happy to see a login screen this morning! It /was/ updating to Win 10, and the update failed. So current status is: improved. I can now check Windows Update without freezing the Control Panel, and several updates updates have downloaded and installed correctly; but the Win 10 update has failed four times now.
I'm re-trying to install Win 10 by DVD, and it's currently checking for updates, which I suspect may take a few hours, if past experience is any indication; but I anticipate that ultimately this installation will also fail.
When I began the installation this morning, I put the DVD in and then rebooted, being greeted with with an expected screen, and continued. When asked for product key, the key I found on the bottom of the computer was not accepted by Windows (the key was double checked for accuracy), and I was instructed to reboot without the disk, and then re-insert it to continue, which I did. A second time the product key was not accepted, but I was given an opportunity to skip it, which I did. And so I continue to wait.
On the side, when I upgraded my own Win 8.1 computer, I had a similar issue with it not accepting the product key, and I ended up waiting for the upgrade through Windows Update; so I wonder how far one can go in the install via media process before it insists on having a product key, and what happens if it doesn't accept it...