Hi,
I've solved all my problems, but when a user that never logged access to my site there is a login modal:

Your answer was:
This is ajax login box. Open when you access Jomsocial page that need to be logged in . It's auto defined in core files and will show whenever session expired and you are on a Jomsocial page.
If I want to don't see it shown for people that access my site for the first time what can I do?
I can accept for the session timeout but when an unregistred user access it cover my first page that is used to publicize the site
Thanks!