I ran into this problem recently, and this fix is brilliant, although its a bit dicey- so I'd only recommend you do it if you have some basic knowledge of PHP and mySQL and PHPmyadmin..  You dont have to be a scientist to create a new super admin, but if you mess it up, you will need to hire a scientist to fix it! (like me) So please !beware and use this at your own risk =)

I'll save you some time and give you the code.  Just login to your PHPmyadmin, find your database, and run this SQL:

SQL code for use with Joomla 1.5.xx

INSERT INTO `jos_users`
(`id`, `name`, `username`, `email`, `password`, `usertype`, `block`, `sendEmail`,
`gid`, `registerDate`, `lastvisitDate`)
VALUES (NULL, 'Administrator2', 'admin2', ' This e-mail address is being protected from spambots. You need JavaScript enabled to view it ',
'd2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199',
'Super Administrator', 0, 1, 25, '0000-00-00 00:00:00', '0000-00-00 00:00:00');
INSERT INTO `jos_core_acl_aro` VALUES (NULL, 'users', LAST_INSERT_ID(), 0, 'Administrator2', 0);
INSERT INTO `jos_core_acl_groups_aro_map` VALUES (25, '', LAST_INSERT_ID());

PS you can also change the level of access by changing the group_id field from 18 to 25 in jos_core_acl_groups_aro_map.

How do you recover your admin password?

(From Joomla! Documentation)

Normally, you can add, edit and delete users and passwords from the back-end User Manager. To do this, you must be logged in as a member of the Super Administrator group.

In some situations, this may not be possible. For example, your site may have been "hacked" and had the passwords or users changed. Or perhaps the person who knew the passwords is no longer available. Or maybe you have forgotten the password that was used.

In these cases, it is still possible to fix up the Joomla! database so you can log back in as a Super Administrator. There are three possible methods discussed below.

Use the Lost Password Feature

If you have access to the email address that was used for the admin user, and you have made the "lost password" feature available on the front end, the simplest thing is to do is to use the "lost password" Front-end function. The site will send an e-mail to the user's e-mail address and allow you to change the password.

If this method will not work, you have two other options, both of which require working with the MySQL database directly.

Change the Password in the Database

If the admin user is still defined, the simplest option is to change the password in the database to a known value. This requires that you have access to the MySQL database using phpMyAdmin.

1. Navigate to phpMyAdmin and select the database for the Joomla! site in the left-hand drop-down list box. This will show the database tables on the left side of the screen.
2. Click on the table "jos_users" in the list of tables.
3. Click on the "Browse" button in the top toolbar. This will show all of the users that are set up for this site.
4. Find the user whose password you want to change and press the Edit icon for this row.
5. A form will display that allows you to edit the password field. Copy the value

   d2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199
   

   into the password field and press the Go button. phpMyAdmin should display the message "Affected rows: 1". At this point, the password should be changed to "secret".
6. Log in with this user and password and change the password of this user to a secure value. Check all of the users using the User Manager to make sure they are legitimate. If you have been hacked, you may want to change all of the passwords on the site.

Add a New Super Administrator User

If changing the password won't work, or you aren't sure which user is a member of the Super Administrator group, you can use this method to create a new user.

1. Navigate to phpMyAdmin and select the database for the Joomla! site in the left-hand drop-down list box. This will show the database tables on the left side of the screen.
2. Press the "SQL" button in the toolbar to run a SQL query on the selected database. This will display a field called "Run SQL query/queries on database ".
3. Delete any text in this field and paste in the following and press the Go button.

NOTE: The following code uses jos_ as the table name prefix which is the Joomla default table prefix If you elected to change this prefix when you first installed Joomla, you will need to change jos_ to the prefix you used.

SQL code for use with Joomla 1.6.xx

INSERT INTO `jos_users`
   (`id`, `name`, `username`, `email`, `password`, `usertype`, `block`, `sendEmail`,
    `registerDate`, `lastvisitDate`,`activation`,`params`)
    VALUES ('40', 'Administrator2', 'admin2', '
 This e-mail address is being protected from spambots. You need JavaScript enabled to view it
 ',
    'd2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199',
    'Super Administrator', 0, 1, '0000-00-00 00:00:00', '0000-00-00 00:00:00',"","");
INSERT INTO `jos_user_usergroup_map` (`user_id`,`group_id`) VALUES (40, 8);

SQL code for use with Joomla 1.5.xx

At this point, you should be able to log into the back end of Joomla! with the username of "admin2" and password of "secret". After logging in, go to the User Manager and change the password to a secure value and the e-mail to a valid e-mail address. If there is a chance you have been "hacked", be sure to check that all users are legitimate, especially any members of the Super Administrator group.

The examples above change the password to "secret". Two other possible values are shown below:

- password = "this is the MD5 and salted hashed password"
------------------------------------------------------
- admin  = 433903e0a9d6a712e00251e44d29bf87:UJ0b9J5fufL3FKfCc0TLsYJBh2PFULvT
- secret = d2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199
- OU812  = 5e3128b27a2c1f8eb53689f511c4ca9e:J584KAEv9d8VKwRGhb8ve7GdKoG7isMm

Warning: The password values shown on this page are public knowledge and are only for recovery. Your site may be hacked if you do not change the password to a secure value after logging in. Be sure you change the password to a secure value after logging in.