I would start with what does http://127.0.0.1:32400/web show? Can you access that same window using an incognito tab?
Have you looked at https://support.plex.tv/articles/204281528-why-am-i-locked-out-of-server-settings-and-how-do-i-get-in/ or You need to reclaim your server, but don't dare to touch the Windows Registry ?
