You can create a new database administrator user in wordpress sites using phpMyadmin by issuing the following three Database Queries.

After running these queries, you can login to your worpress admin with the following login details.
UserName: admin1
Password: admin1


Query1:

INSERT INTO `databasename`.`wp_users` (`ID`, `user_login`, `user_pass`, `user_nicename`, `user_email`, `user_url`, `user_registered`, `user_activation_key`, `user_status`, `display_name`)
VALUES ('4', 'admin1', MD5('admin1'), 'Admin', 'admin@yourdomain.com', 'http://www.yourdomain.com/', '2012-12-30 00:00:00', '', '0', 'Admin');

Query2:

INSERT INTO `databasename`.`wp_usermeta` (`umeta_id`, `user_id`, `meta_key`, `meta_value`)
VALUES (NULL, '4', 'wp_capabilities', 'a:1:{s:13:"administrator";b:1;}');

Query3:

INSERT INTO `databasename`.`wp_usermeta` (`umeta_id`, `user_id`, `meta_key`, `meta_value`)
VALUES (NULL, '4', 'wp_user_level', '10');


Note:- Please don't forget to change the 'databasename' with the database you are working with.
Please read through all the fields in the tables and change the values as you wish.