$query->num_rows nothing returns

If it's true that your table name is in lower case and the fields are in firstcaps, then the next question is: do you really want to look for records that literally hold the values 'user' and 'password', or - which is more likely - do you want to get records that match a certain combination of username and password?
In that case, your query should look like this:

PHP Code:

$query = $this->db->query("SELECT * FROM `usuario` WHERE `Usuario` = '$user' AND `Senha` = '$password'");