There is no root account.. plesk changes it to admin and use the PSA admin password!
If that doesnt work, do this to reset the admin password
1. Take down the mysqld server by sending a kill (not kill-9) to the mysqld server. The pid is stored in a `.pid' file, which is normally in the MySQL database directory:
shell> kill `cat /mysql-data-directory/hostname.pid`
You must be either the Unix root user or the same user mysqld runs as to do this.
2. Restart mysqld with the --skip-grant-tables option.
3. Set a new password with the mysqladmin password command:
shell> mysqladmin -u root -p'mynewpassword'
4. Now you can either stop mysqld and restart it normally, or just load the privilege tables with:
shell> mysqladmin -h hostname flush-privileges
5. After this, you should be able to connect using the new password.
Alternatively, you can set the new password using the mysql client:
1. Take down and restart mysqld with the --skip-grant-tables option as described above.
2. Connect to the mysqld server with:
shell> mysql -u root mysql
3. Issue the following commands in the mysql client:
mysql> UPDATE user SET Password=PASSWORD('mynewpassword') WHERE User='admin';
mysql> FLUSH PRIVILEGES;
4. After this, you should be able to connect using the new password.
5. You can now stop mysqld and restart it normally.
Have fun!!