Nonnatus,
I have Dell support and they could not figure out why this was happening on my computer.
The only solution I found was to re-install a clean version of Windows 8.1, run all 193 Windows updates (with multiple reboots) and then install a clean version of Windows 10.
Of note:
Because there may have been corrupted files in my Windows 8.1, an upgrade could have carried over those corruptions to Windows 10, so a clean install was needed.
I could not roll back to 8.1 (despite Microsoft assurances that I could), so Dell sent me a Windows 8.1 install on USB media. I also downloaded a Windows 10 install on USB media myself from Microsoft.
After the Windows 8.1 was re-installed and all the updates made, I looked for the confirmation that I was now Windows 10 eligible (icon in lower right tray). When it didn't appear, I ran a troubleshooter which told me that a key
needed Windows update (KB2976978) was not installed, although I confirmed it was. I also searched the Microsoft site for solutions on this point without success. I decided to run the Windows 10 install anyway, and it was successful.
I also noted an odd thing with the Windows OS Product ID. Being cautious, when I did the original upgrade to Windows 10, I took down the Product ID info (Under /Control Panel/System and Security/System. However, during the second
Windows re-install/set-up, it would not accept this Product ID and responded that zeros and ones (0 and 1) were not acceptable digits for the Product ID. Luckily, it allowed me to continue the set-up through to successful completion without entering it. After
install, a Product ID was "magically" in place (not by me) and Windows was activated. Of note, this Product ID also had zeros and ones (0 and 1) .
Because I did a clean install, I made sure to first back up all my files on an external hard drive, since all this data would be overwritten. Don't forget to do the same.
Best of luck with finding solutions.
A clean install may be your best option. It may also be your only option.
Rene