If you find that your PIN does not work & will not let you sign in to Windows 10, then see this post. It will also help you if you cannot change the PIN. It is quite possible that your PIN file may have got corrupted or that the PIN may not have been preserved after an upgrade.
Cannot change PIN or PIN does not work in Windows 10

To rectify this situation, log into your Windows 10 computer using an alternative sign in option, and then do the following:
Create a system restore point. Then open File Explorer and browse to the following location –
C:\Windows\ServiceProfiles\LocalService\AppData\Local\MicrosoftClick on
Ngc folder to open it. You will be denied permission to access this folder. Click on the ‘security tab‘ link to open the Properties box of this folder. You will now have to take Full Ownership of this Folder.
Once you are given access to the folder and you open it, press
Ctrl+A to select everything, and
delete all the contents of this folder.
This will repair your PIN, by resetting things to default.
Now open the Windows 10
Settings app >
Accounts settings >
Sign-in Options.
Under
PIN, click on
Add a PIN. Enter your
new PIN and click
OK.
Finally
restart your computer and see. You will be able to sign-in with your new PIN.
You can use this procedure when you face any problem with your PIN – even when you cannot change your PIN or if PIN does not show up as a sign-in option on your logon screen.
twc