A modified version of option 3 on this page worked for me. I tried option 4 first since it is a built in windows "startup repair" option but it didn't work. Option 3, deleting a particular system folder, did.
The modification came from the fact that even safe mode requires the pin and so you can't log in and use explorer like it says in the article.
- open command prompt (get to windows recovery as detailed in the article. click troubleshoot then click command prompt (instead of startup settings))
- switch to install drive (usually c:) with cd c:\
- if not at the root of the drive (C:>) then type cd .. {enter} until you are
- type cd Windows\ServiceProfiles\LocalService\AppData\Local\Microsoft
- type rd /S Ngc (deletes directory containing sign in option data)
- restart the machine and you will be asked to login with password and create new pin
- recommended: once in, open settings and find sign in options. turn off the option "only allow Windows Hello..." . This will allow you to select password sign-in when needed (assuming it doesn't get corrupted too).
That fixed it immediately for me. Other options in the article worth looking at, including what to do if you need to wipe it.