Start Windows 10 in safe mode and then run TB. If TB runs OK, there is some other program launching at normal Windows start causing the problem, possibly a security program. When TB 'just doesn't work', what error messages or outcomes do you see?

The problem is NOT with Thunderbird. After spending 2 days trying to resolve this issue, I've determined that the problem resides in Windows itself. Windows no longer retains program settings such as country and locale, entry fields in System do not accept typed input, TrueType font display does not hold through reboot. Microsoft Office is trashed - missing modules. Time to bite the bullet and re-install Windows. There goes another 3 days of my life.

Thanks for looking at this problem and thinking about it.