A good start would be to log off the server, and the plex.tv site, and all players on tablets, TVs, etc. Shut down and Restart the server on your platform and log on. You may be prompted to claim your server. Once on the https://app.plex.tv/desktop/#!/ go to settings. If all is well, you can log on t all the other devices
Download and install the current version of Plex Media Server.
After the installer finishes, login to Plex Media Server locally.
If on the same system as Plex: http://127.0.0.1:32400/web
If on a different system on the same network: http://plex_server_ip_address:32400/web
(Ex: if the IP address of your server is 10.11.12.13, go to http://10.11.12.13:32400/web).
You should be able to login and claim your server.
If you see a “503” message that Plex is performing maintenance, then wait for it to finish. Plex is migrating the server database. If you stop the process you risk database corruption. Also, Plex will restart the migration process the next time it is launched.
Follow the directions to completely remove Plex from your PC.
This includes the application, registry entries, and Plex Data Folder.
Do not delete your Plex account.
Do not delete your media files.
Download and install the current version of Plex Media Server.
If you run into issues, report back before you start uninstalling/re-installing, deleting any files, registry entries, etc.
If possible, include a set of server log files with your post.