If you find that your PIN does not work & will not let you sign into 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, create a system restore point first and then 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 –
Click 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.
Ultimate Windows Tweaker will let you add the Take Ownership of Files and Folders easily to Windows context menu. You will find it under Context Menu section > Desktop Context Menu 2 tab.
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 login screen.