What happens when you try to log in?

nothing happens.
don't show any error messages.

I'm sorry, but there isn't enough info here to help you effectively.

Please try with plugins disabled and see if that works. Core doesn't have this bug, so it is either in your server config, or a plugin, or you are mistyping your password, or something else.

But as you can see the range of possibilities is a bit large. So we need more info to narrow it down.

First suggestion (as Evan has already written): try with 3rd party plugins temporarily disabled (especially any plugins that might modify the login process).

Have you installed your site entering "vaicapinar.com.br" (without "www") as site url and are now trying to login at "www.vaicapinar.com.br" or vice versa? If that's the case, what happens when you enter the same url you used as site url to login? If it works then you might follow the instructions at http://learn.elgg.org/en/1.9/appendix/faqs.html?highlight=login%20mismatch#login-token-mismatch to get the login working also for the other case respectively.