What you should have done was
1 - backup Plex Media Server folder
2 - backup registry
3 - reinstall Windows
4 - install PMS
5 - restore Plex Media Server folder to the same location as before
6 - import the backup registry
The registry points to where the files in step 5 are. If you restore to the wring location, then it won’t find the files and will appear to be a new server. If you placed 5 into the wrong location, then you need an additional step.
7a - Open Plex Web, under settings \ Server \ General \ The path where local application data is stored, enter the path to 5. Restart PMS.
or 7b - Edit the registry, find the entry that shows the path to 5, edit it. Restart PMS.
