If I had a system with this frustrating problem, I'd try a Windows 10 repair-upgrade.
This trick has solved several equally frustrating problems for me, including apparently clean Windows 10 systems with healthy twin brothers.
The repair-upgrade "upgrades" the existing Windows 10 system to a clean Windows 10 system, preserving most programs and settings.
You might have to reinstall AC afterward.
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Briefly, a repair-upgrade does not require you to boot from a DVD or USB. In fact, it won't work that way.
Instead, you start your computer, download the W10 iso, click on it to mount it, and run setup.exe:
https://answers.microsoft.com/en-us...ows/35160fbe-9352-4e70-9887-f40096ec3085
