Hello Narmah. I'm Greg, here to help you with this.
It should not ask for a PIN, it should ask for a password. Check the wording, then look for a link nearby for Sign In Options to try to change to password. This link should appear wherever you are asked to sign in. If not the account may be corrupted.,
But a UAC box should not ask for a password unless you're a Standard User. If you're the owner of the PC then you should be using an Administrator account. It is a myth that you're safer running under Standard account on your own PC.
Windows will pop up a UAC box in either type account if changes are attempted to be made from within or outside. The only difference is that the Admin has a yes (approve) button while a Standard account must put in the Admin password to proceed, unnecessary make-work with no security advantage.
This is why Windows installs an Admin account or a new PC sets up an Admin account because it assumes you're the owner, and the owner should always have an Admin account.
Based on the answers you post back I may have other suggestions.
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