blank white screen

        <?php
            session_start();
            require '../inc/connection.php';

        if(isset($_SESSION['logged_in'])){
                //echo "Dashboard";
                 include 'templates/header.php';
                 ?>

              <div class="list-group">
                <div class="list-group-item">

                    <a class="list-group-item" href="add.php">
                        <h4 class="list-group-item-heading">Add Post or Article</h4>
                        <p class="list-group-item-text">
                     Create New post or article to your CMS blog system with pdo way</p>
                    </a>

                    <a class="list-group-item" href="delete.php">
                        <h4 class="list-group-item-heading"> Delete Post or Article</h4>
                        <p class="list-group-item-text"> Delete Old post or article from your CMS blog system with pdo way  </p>
                    </a>

                    <a class="list-group-item active" href="logout.php">
                        <h4 class="list-group-item-heading">  Logout</h4>
                        <p class="list-group-item-text">  Logout and go have some fun</p>
                    </a>

                </div>
            </div> <!-- End list-group -->

        <?php
        include 'templates/footer.php';
            }else{


            if(isset($_POST['username'], $_POST['password'])){
                    $username = $_POST['username'];
                    $password = $_POST['password'];
                            if(empty($username) or empty($password)){
                            $error = 'Username or Password Empty';
                            }else{

        $query = $pdo->prepare("SELECT * FROM `users` WHERE username=? AND password=? ");
                        $query->bindValue(1, $username);
                        $query->bindValue(2, $password);
                        $query->execute();
                        $num = $query->rowCount();

                        if($num == 1){
                            $_SESSION['logged_in'] = true;
                            header('Location: index.php');
                            exit();
                        }else{
                            $error = 'Wrong Username or Password';
                        }

            }//else
        }
        include 'templates/header.php';

        if(isset($error))
                    echo "<p class='bg-danger btn-lg'> $error </p>";



        ?>
        <form action="index.php" method="post" rol="form">

        <div class="form-group">
                    <label for="">Username : </label>
           <input class="form-control" name="username" placeholder="username" type="text">
                </div>

                 <div class="form-group">
                    <label for="">Password : </label>
         <input class="form-control" name="password" placeholder="password" type="password">
                </div>

                <input class="btn btn-info btn-lg btn-block" value="Login" type="submit">
            </form>

            <?php
            include 'templates/footer.php';
         ?>
        <?php   } ?>