Microsoft Account Password Suddenly Required

[daw]

Wake up this morning and wife's PC demands a Microsoft Password in order to operate the computer. I know nothing of Microsoft passwords - never needed one before. The solution: Log on to the Internet to reset the password -- BUT you cannot log on to anything without the password. Research on another computer reveals the cute trick of holding down the shift key while restarting in order to get back to a previous build of Windows - BUT you need to do this as an administrator - which you can do by signing into Windows - FOR WHICH YOU NEED A PASSWORD!

 

[Trouble]

I know nothing of Microsoft passwords - never needed one before.

Not the first time we've seen this problem, and.....
I'm not sure that there is an easy solution.
Some people report that rebooting the computer multiple times seems to clear this.
At the sign-in screen near the bottom left do you see any other accounts listed?
At the sign-in screen do you see any clickable links or back arrows where you might be able to evoke alternate sign-in options, or.....
Anything that might indicate "I'm not" or "Not me" or words to that affect referencing the user account present on the sign-in screen that is requesting the password?
Is the user account that is showing, indicating a Microsoft account or other email address that may have, at some point been linked to the local user account?
Are you certain that it is not prompting for a PIN number instead of a password?