If MySQL still refuses to start check the log file for error messages. 

If you see this error, or a similar error with your mysql.user table

2018-09-06T14:39:07.778314Z 0 [ERROR] Fatal error: mysql.user table is damaged. Please run mysql_upgrade.
2018-09-06T14:39:07.778359Z 0 [ERROR] Fatal error: Failed to initialize ACL/grant/time zones structures or failed to remove temporary table files.
2018-09-06T14:39:07.778614Z 0 [ERROR] Aborting

Do the following …

You can’t run a MySQL database upgrade because your MySQL server does not start in the first place, you could try to add the line “skip-grant-tables” to your MySQL configuration file at the end of the section “[mysqld]” and then try to restart the MySQL server. This will tell the server to ignore your defective users table during startup so it can be upgraded afterwards.

To add this in MAMP PRO, open your MySQL template file. Go to File > Edit Template > MySQL > my.cnf 


Now start your servers.

The server should start and you should be able to perform a database upgrade via the MAMP PRO main menu “Tools > Upgrade MySQL Databases”.

Don’t forget to remove the added line afterwards and restart your MySQL Server.