It does look like you need to reinstall the PMS software; once that happens, you can see about re-creating your libraries.
First, I would make sure the Plex Media Server is not running on your Windows computer. If it is, stop it first, and try to restart it.
If it’s not running, you could try starting it again. You will need to do this from your Windows computer and not from another device.
If that doesn’t work, then download and install the PMS software.
With luck, your metadata is intact and your libraries might show up; otherwise you might have to recreate them by re-adding folders from your computer.