How to delete mysql databases?

[Nachteule]

1) You should have a look into Kodi logfile(s)
2) Check you mysql database (I'm not db expert, but I'm sure google is your friend)
3) Check fs of your db server, maybe fs is corrupt or disk is broken

Back to your first question: Removing database files in /home/xbian/.kodi/Database is very bad idea, because in case of using common mysql db the relevant local db files are not used and should not exist locally