Problema con PDO e login

[fermat]

apportate queste modifiche funziona:

    public function login($user, $pass) {
        $pass = sha1($pass);
        $strQuery = "SELECT * FROM user WHERE user_name='" . $user . "' AND user_pass='" . $pass . "'";
        try {
            $query = $this->pdo->prepare($strQuery);
            $query->execute();
            if ($query->rowCount() == 1) {
                $_SESSION['login_eseguito'] = TRUE;
                $_SESSION['user_id'] = $result->user_id;
                return TRUE;
            } else {
                return FALSE;
            }
        } catch (PDOException $e) {
            print "Error!: " . $e->getMessage() . "
";
            die();
        }
    } 

ho usato un'istruzione preparata in pratica.