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Having issues with a log in page using PHP
<Doctype HTML>
<html>
<head>
<?php

//include the required functions

include(' ./includes/functions.php');

//make connection
$db = conn();

//check for username and password
if(isset($_POST['username']) && isset($_POST['password'])) {

//Query the db for the user

$result = $db->query("SELECT * FROM users WHERE username ='{$_POST['username']}'");

//fetch the result set
$row = $result->fetch_assoc();

//check credentials again the database
if ($result == true && md5($_POST['password']) == $row['password']){

//store user as seesion variable
$_SESSION['valid_user'] = $_POST['username'];

/*
* @Locations:
* /admin, /calc, /live
*
* @Authorization Levels
* 1 = production employee
* 2 = Quality tech
* 3 = Management
* 0 = not authorized
*
* @var = $row['active']
*/

if ($row['active'] == '3') {
  header('Location: ./admin/index.php ');
}
elseif ($row['active'] == 2) {
  header('Location: ./calc/index.php ');
}
elseif ($row['active'] == 1) {
  header('Location: ./live/data.php ');
}

}
elseif ($_POST['password'] != $row['password']) {
   echo ('Password Incorrect');
}

}
else
{

?>

<style type="text/css">

body
{
margin: 0;

/* IE10 */
background-image: -ms-linear-gradient(bottom, #FFFFFF 0%, #7EBC50 100%);
background-repeat: no-repeat;

/* Mozilla Firefox */
background-image: -moz-linear-gradient(bottom, #FFFFFF 0%, #7EBC50 100%);
background-repeat: no-repeat;

/* Opera */
background-image: -o-linear-gradient(bottom, #FFFFFF 0%, #7EBC50 100%);

/* Webkit (Safari/Chrome 10) */
background-image: -webkit-gradient(linear, left bottom, left top, color-stop(0, #FFFFFF), color-stop(1, #7EBC50));

/* Webkit (Chrome 11+) */
background-image: -webkit-linear-gradient(bottom, #FFFFFF 0%, #7EBC50 100%);

/* Proposed W3C Markup */
background-image: linear-gradient(bottom, #FFFFFF 0%, #7EBC50 100%);

/* IE6-IE9 */
filter: progid:DXImageTransform.Microsoft.gradient(startColorStr='#7EBC50', EndColorStr='#FFFFFF');

}

#login
{
background-color: #FBFBCA;
width: 15em;
margin-right: auto;
margin-left: auto;
margin-top: 15%;
margin-bottom: auto;
border: 2px solid #3A8E00;
border-radius: 5px;
text-align: center;
padding-bottom: 1em;
box-shadow: 10px 10px 5px #888888;
-moz-box-shadow: 10px 10px 5px #888888;
}

#login .text, h4
{
color: #1C4F00;
font-family: "Helvetica Neue", "Lucida Grande", "Segoe UI", Arial, Helvetica, Verdana, sans-serif;
}

</style>

<title>LLF Lab || Login Page</title>

</head>

<body>

<div id="login">

<h4>LLF Lab Login</h4>

<form action="login.php" method="post">

<span class="text">Username:</span><br />

<input type="text" name="username"/><br />

<br />

<span class="text">Password:</span><br />

<input type="password" name="password"/>

<br />

<br />

<input type="checkbox" name="rememberme"/><span class="text">Remember me</span>

<br />

<br />

<input type="submit" value="Login" />

</form>

</div>

</body>

</html>

<?php

}//endif ?>

<Doctype HTML>
<html>
<head>