Discussion of article Empty, white page by accessing Plesk panel - No access - Error 500:
QuoteNo access to Plesk Panel - Error 500 - What to do now?
MySQL server doesn't start?
Solution: You have to delete MySQL socket! The rebirth of the MySQL socket.
Only two little commands are the ultimate solution after an unsuccessful start of MySQL server and the entire Plesk panel.
Have fun with the following solution. Knowledge is power.