我无法执行这个PHP代码(HTML)

所以我之前使用过这个，但现在当我使用它与一些不同的代码(Extras)。当我点击"Login"按钮时，我似乎无法运行PHP代码。

有人知道哪里出了问题吗?

<?php
    require('process.php'); //Remember $username and $password taken as variables
    $ok = 0; //Assume nothing is ok, collect evidence to prove otherwise
    if(isset($_POST["submit"])) {
        //Submit clicked, user possibly logged in - check
        $who = $_POST['nick'];
        $pw = $_POST['pass'];
        $verify = 'select * from users where user ="' . $who . '"';
        $answertable = mysql_query($verify, $connection);
        if (!$answertable) {
            echo 'Invalid username or password';
        } else {
            list($usr, $pwd) = mysql_fetch_row($answertable);
            if (MD5($pw) == $pwd) {
                $ok = 1; //Valid user and password, It's A OK
                echo 'Welcome ' . $usr;
                //Do stuff here because you are a valid user
                echo '<br><a href = "login.php">Logout</a>';
                } else {
                    echo 'Invalid username or password, please try again<br><br>';
                }
            }
     }
     if (!$ok) { //Either login was wrong or not yet tried
       ?>      <!-- Present from to gather login details -->
         <div id="dialog" style="width: 350px; background-color: #FFFFFF; margin: 50px auto; border-radius: 15px; padding: 5px 15px 5px 15px;">
             <form role="form">
                 <div class="form-group">
                     <h2><center>Webmaster login</center></h2>
                 </div>
                 <div class="form-group">
                     <p>Enter your username:</p>
                     <input id="nick" class="form-control" placeholder="Username"/>
                </div>
                <div class="form-group">
                    <p>Enter your password:</p>
                    <input id="pass" class="form-control" type="password" placeholder="Password"/>
                </div>
            </form>
            <hr/>
            <div class="form-group">
                <form method="post" action="index.php">
                    <button type="submit" id="loginbtn" class="btn btn-play btn-primary">Login</button>
                </form>
            </div>
            <br clear="both"/>
            <hr/>
         </div>
         <?php
         }
         ?>

Process.php

<?php
/* Set the connections to the database */
$host = 'localhost';
$username = 'root';
$password = '';
$dbname = 'login';
/* Build a bridge to the server */
$connection = mysql_connect($host, $username, $password) or die('Problems connecting');
/* Connect to the database through the bridge */
mysql_select_db($dbname) or die('Problems finding the database');
?>