"ERROR 1045 (28000): Access denied for user 'admin'@'localhost' (using password: YES)" when performing any changes in Plesk or in database directly

Make sure that the admin user has all privileges:

• Log into MySQL server:

  # MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql -u admin mysql
  

• Check admin privileges:

  mysql> SHOW GRANTS FOR 'admin'@'localhost'\G
  

• Grant all privileges toadmin if required:

  GRANT ALL ON *.* TO 'admin'@'localhost' WITH GRANT OPTION;
  FLUSH PRIVILEGES;

• 
  check/var/log/mysqld.log.
  
  
  If you see a message such as:
  [ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it
  
  
  this probably means that MySQL was reinstalled or was not upgraded completely. Run the following command to update MySQL:
      MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql_upgrade -uadmin