Displaying blank page after inserting PHP code in between DIV tags, the code is as follows:

<!DOCTYPE html>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>Bulk Sms</title>
    <link rel="stylesheet" href="css/styles.css" type="text/css">
        <link rel="stylesheet" href="css/responsive-nav.css">
    <script src="js/responsive-nav.js"></script>

    <div class="inner">
<a href="index.php">
<img src="images/logo.png" alt="Bulk Sms" border="0"></a>
        <section class="top-nav">
    <div  class="nav-collapse">
                    <li><a href="index.php" title="Home">Home</a></li>
                    <li><a href="javascript:void(0);" onClick="view_contents('about');" title="About Us">About</a></li>
                    <li><a href="javascript:void(0);" onClick="view_contents('pricing');" title="Prices offred">Pricing</a></li>
                    <li><a href="javascript:void(0);" onClick="view_contents('contact');" title="Contact me">Contact</a></li>
                    <li><a href="login.php" title="Login">Login</a></li>
                    <li><a href="register.php" title="New user Registrarion">Create Account</a></li>

    <div class="bruce-banner">
        <img src="images/banner.jpg" align="bulk_sms" border="0"/>           
          <div class="login_register_stuff">
            <div id="login_panel">

              <div class="inner-container login-panel">
             <?php // The actual problem begins from here

                if(isset($_GET['error'])) {
                echo 'Wrong username or Password';

              if(isset($_GET['msg']) {
              echo 'Registered successfully. Please Login. Check your email for password.';
                     <h3 class="m_title">Login</h3>
                <form action="login-check.php" id="login_page" name="login_page" method="post" onSubmit="return validate(this);">
                  <input type="text" id="uname" name="username" class="inputbox" placeholder="Username">
                  <input type="password" id="upass" name="password" class="inputbox" placeholder="Password">
                  <input type="submit" id="login" name="submit" value="LOG IN">
                </form>                <div class="links"><a href="forgot-password.php">FORGOT YOUR PASSWORD</a> <br>
                 <div class="createacc"><a href="register.php" class="create_account">CREATE ACCOUNT</a> </div>
            <!-- end login panel -->

    <div class="inner">
        <section class="bulksms">
            <p id="main_area"></p>

    <footer role="contentinfo" id="footer">
        <div class="inner copyright">
            <small>© 2013 BULK SMS. All Rights Reserved.</small>
      var navigation = responsiveNav(".nav-collapse", {
        animate: true,        // Boolean: Use CSS3 transitions, true or false
        transition: 250,      // Integer: Speed of the transition, in milliseconds
        label: "Menu",        // String: Label for the navigation toggle
        insert: "after",      // String: Insert the toggle before or after the navigation
        customToggle: "",     // Selector: Specify the ID of a custom toggle
        openPos: "relative",  // String: Position of the opened nav, relative or static
        jsClass: "js",        // String: 'JS enabled' class which is added to <html> el
        init: function(){},   // Function: Init callback
        open: function(){},   // Function: Open callback
        close: function(){}   // Function: Close callback

Line 47: if(isset($_GET['msg']) { should be if(isset($_GET['msg'])) { missing a parentheses. Do you have errors turned off?

lots of Thanks toxicandy, it's solved