by Luis de Vasconcelos.
What do you mean by "no main site administrator"? What happened to your "site administrator" account? Have you just forgotten the password? Or was the admin account somehow deleted?
To recover your admin password just search this forum for something like "forgot admin password". The question has been asked a million times so there are lots of hits. You'll get results like:
http://docs.moodle.org/26/en/Administration_FAQ#I_have_forgotten_the_admin_password
https://moodle.org/mod/forum/discuss.php?d=18103
