It does not have a banner that says it found an unclaimed server on your network?
try the link given above by ottokerner. https://support.plex.tv/articles/204281528-why-am-i-locked-out-of-server-settings-and-how-do-i-get-in/
after removing those registry settings restart the windows computer and launch the server on it.
then go to https://app.plex.tv sign in and see if it asks you to claim.
you can also try this one of our Ninja volunteers made [REL] ClaimIt
