I know it's a stupid question... I just update my server yesterday night (late night) and didn't save the admin page I was working.
This morning I cant login, since my foruns are closed...
how can I login?
Thank you

The link should still be there, even if they are closed. Unless you removed it.

You should be able to get the login page by adding /login.php to the end of your URL.

Found why:
if I'm using Firefox, and go to www.mysite.com/forum/admin/logon/php it is not redirecting to the login page, instead it point to the message "The forum is closed" and that's it.
If I'm usiing Exploerr, then going to www.mysiete.com/forum/admin/logon.php shows the forum is closed, by then, redirects to the right logon page.
Is it a bug?

That's not the correct link to the login page. That's the main page of the control panel. You can't login directly there.

Visit your forum and click login.
http://www.mysite.com/forum/login.php

Then you will be able to visit the control panel by clicking on the control panel link.