MD5 Hashed Passwords web item mall now not work

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hi there i just used Hashing/ MD5 password format but i noticed my webmall dose not longer work is there a easy fix to make it accept the MD5 hashed passwords here is my login Script

 Spoiler

<?php
if (isset($_POST['login'])) {
$post_data = do_request($_POST, true);
$back_url = 'index.php';

if ($_POST['js_enabled'] != 1)
set_msg('You must have javascript enabled in yout browser', 'error', $back_url, 'login_msg');


if (!$post_data)
set_msg('Please fill all fields', 'error', $back_url, 'login_msg');

$query = mssql_query("SELECT RowID FROM PS_UserData.dbo.Users_Master WHERE userID = '{$post_data['username']}' AND Pw = '{$post_data['password']}'");
if (mssql_num_rows($query) <= 0)
set_msg('Bad username and/or password', 'error', $back_url, 'login_msg');

session_regenerate_id();
write_session('username', $post_data['username']);
write_session('userHA', md5(md5($_SERVER['HTTP_USER_AGENT']).md5($config['home_url']).md5($config['random_code']).$post_data['username']));
redirect('index.php?cat=1', true);

}
?>

echo $back_url

i used this link/scripts if any 1 could help me would be awsum thanx

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all sorted thanx so much