Ran into a mysql issue at work today after an unplanned power outage took the server down. The error was "Fatal error: Can’t open and lock privilege tables: Table ‘mysql.host’ doesn’t exist" everytime we tried to start mysql. Looked like the system tables were gone.
The fix;
We recreated the system tables in the mysql data directory using mysql_install_db.
mysql_install_db –user=mysql –ldata=/mysql-data/location
Restart mysql and you should be good to go.