romsonCheck your "wp_usermeta" table in phpmyadmin. Look under the tabs "user_id" and "meta_key". User ID 1 is usually the first admin, you. Now look for the line "wp_capabilities" under the "meta_key" tab. It should give a "meta_value" of "a:5:{s:13:"administrator";a:1;}" or something like that. Most important is the administrator role. Now look for other user id's with the same administrator role. Delete these lines and user and you should be "hidden admin user" free.
ArtWave