White screen when logging in php

I believe you are not passing "Logar" to $_POST['logar'] .

Test the POST that is being sent in the file logar.php using var_dump($_POST) and check the value being passed.

You may not be entering this if :

if (@$_POST['logar'] == 'Logar') { ... }

Since your input[type="submit"] is passing "Sign Up" :

<input type="submit" class="btn btn-login" name="logar" id="logar" value="Sign Up" />

I testing worked with the name "Submit" this way

<input type="submit" class="btn btn-login" name="Enviar" value="Enviar" />

But I need it to be Sign Up , do you have any idea what's wrong?