Here’s the situation, you, client, webmaster, pet or whoever was playing with users and roles in your favorite store and deleted only main admin account or broke admin account privileges. If it happened to you and you’re locked out from your Magento store, read on.
This script creates new admin user associated to new Inchoo role with all privileges set. Of course, you have to have FTP access for this to work.
Download newadmin script, unpack it, open newadmin.php file (notepad will do) and define username, email and password of the new user. Username and email must be UNIQUE in Magento, so use some new ones and not the old ones that are already in the system, you’ll change it later after you login.
Connect with FTP and copy newadmin.php file to root of your store and run it through web browser like
http://www.yourstore.com/newadmin.php
The script will try to delete itself after user is created, but please make sure it’s removed from the server. Code is tested on 1.3.x versions of Magento and I don’t believe it will work on older versions, so please write some feedback.
Regards 
Excellent Job my Friend…. greetings from Mexico…!!!!!
thanks buddy. time saved!!!
Thank you so much! I still do not know how to get back to my old admin with all my info but at least I got the new one so I can use it.
Ivan, you Sir are a scholar and a gentlemen
(for putting together this script AND providing it).
I used it to gain access to the Magento backend again, after the server crashed during a system restore – which had apparently deleted all Magento admins and so we were getting the “Invalid username or password”, although the original login and password were correct.
NOTE: Because the maintenance flag was set during the system restore, we had to manually remove the ‘maintenance.flag’ file to be able to even get to the login page again.
OMG this just saved me, THANK YOU!
Thank you very much for this.