Hello,

Have you access to the DataBase ?

If yes, then you can make a quick workaround by executing this sql:

INSERT INTO res_groups_users_rel (gid,uid) VALUES (3,1);

after executing this sql, you've to log out and log in again, then refresh the page. When you go to settings menu a 'Access denied" message may appear just close it, and hit the users menu, then refresh the page .... 

When the user's record appear modify the administration access through the UI.

Hope this could help ...