My login and registration

// index.php

<?php
// Stops errors from showing
error_reporting(0);

session_start();
    if(isset($_POST['username'], $_POST['password'])){
     require 'core/connect.php';

    $query = dbConnect()->prepare("SELECT username, password FROM Users WHERE username=:username AND password=:password");
    $query->bindParam(':username', $_POST['username']);
    $query->bindParam(':password', md5($_POST['password']));
    $query->execute();

    if($row = $query->fetch()){
    $_SESSION['username'] = $row['username'];
    $_SESSION['password'] = $row['password'];
    header("Location: index.php");
    } else {
        echo '<p style="text-align: center; color: red;">Invalid username/password</p>';
    }

    if($row = $query->fetch()){
        $_SESSION['password'] = $row['password'];
        header("Location: index.php");
        }
    }

    if(isset($_SESSION['username'])) {
                echo '
                <div style="max-width: 90%; text-align: center; margin: 0 auto;">
                <img src="http://i.imgur.com/MBuIZ3h.png" width="75%" style="text-align: center; margin: 10px 0;">
                <p style="margin-left: 8px; font-size: 24px;">Welcome, <strong>'.$_SESSION['username'].'</strong><br></p><p style="margin-top: -20px; margin-left: 10px;"><a href="logout.php">Logout</a></p>
                </div>';
            } else {
                echo '
                <div style="max-width: 90%; text-align: center; margin: 0 auto;">
                    <img src="http://i.imgur.com/MBuIZ3h.png" width="75%" style="text-align: center; margin: 10px 0;">
                    <form method="POST" style="text-align: center; margin: 0 auto;">
                        <input style="width: 100%; margin: 5px 0;" type="text" name="username" placeholder="Username"><br />
                        <input style="width: 100%;" type="password" name="password" placeholder="Password"><br />
                        <input style="margin-top: px; width: 100%;" type="Submit" value="Login"><br>
                        <br>
                        <a href="http://www.heartfx.org/registeraccount.php"><p style="margin-top: -10px;">Register an account</p></a>
                    </form>
                </div>';
            }
        ?>













// core/connect.php


<?php
    function dbConnect(){
        try{
            $dbuser = '';
            $dbpw = '';
            $conn = new pdo("mysql:host=198.71.225.55:3306;dbname=heartfx_users;", $dbuser, $dbpw);
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            return $conn;

        }   catch(PDOException $e){
            echo 'ERROR', $e->getMessage();
        }
    }
?>











// register.php


<form method="POST">
    <?php
    if (strlen(':username')<6) {
        echo "Username must be atleast 6 characters";
    } else {
        echo '<button type="submit" style="width: 100%; padding: 10px 5px;">Register account</button><br><br>';
    }
    ?>
</form>
        </div>

        <br><br>

        <?php
        session_start();

        if(isset($_POST['firstname'],$_POST['lastname'], $_POST['username'], $_POST['password'], $_POST['email'])){
            require 'core/connect.php';

            $query = dbConnect()->prepare("INSERT INTO Users (firstname, lastname, username, password, email) VALUES (:firstname, :lastname, :username, :password, :email)");
            $query->bindParam(':lastname', $_POST['lastname']);
            $query->bindParam(':firstname', $_POST['firstname']);
            $query->bindParam(':username', $_POST['username']);
            $query->bindParam(':password', md5($_POST['password']));
            $query->bindParam(':email', $_POST['email']);

            if (strlen($_POST['username'])<6) {
                echo 'Username must be at least 6 characters';
            } else {
                header("Location: index.php");
            }

            if($query->execute()){
                header("Location: registeredaccount.php");
            } else {
                echo 'ERROR';
            }
        }
        ?>






// logout.php


<?php
    session_start();
    session_destroy();
?>