Find the mysql database folder and backup.

We don't know where you backup-ed your database to, if at all. If you don't know either, you probably didn't. So you can't restore.

If your database is broken beyond repair, the easiest is to just install fresh from scratch. Create a new MySQL database with credentials, remove the local/config/database.inc.php file and then point your browser to install.php

If you're using physical albums, you then could sync again. For virtual albums the files exist under upload/ but there's no association whatsoever to images in albums nor tags, so those somehow would have to be reimported, don't know if there's a plugin or script that would help with that.

Good luck.