Problemas con el usuario y auth scripts de actualización

<?PHP
ob_start();
session_start();

//check that the user is calling the page from the login form and not accessing it directly
//and redirect back to the login form if necessary
if (!isset($username) || !isset($password)) {
header("Location: http://www.mywebsite.com/login.htm" );
}
//check that the form fields are not empty, and redirect back to the login page if they are
elseif (empty($username) || empty($password)) {
header("Location: http://www.mywebsite.com/login.htm" );
}
else{

//set the database connection variables

$dbHost = "localhost";
$dbUser = "(omitted)";
$dbPass = "(omitted)";
$dbDatabase = "(omitted)";

//add slashes to the username and md5() the password
$user = addslashes($_POST['username']);
$pass = md5($_POST['password']);

mysql_connect("$dbHost", "$dbUser", "$dbPass")or die ("Error connecting to database.");
mysql_select_db("$dbDatabase") or die(mysql_error());

$result=mysql_query("SELECT * FROM clients WHERE password='$pass' AND username='$user'") or die("Couldn't query the user-database.");
$rowCheck = mysql_num_rows($result);
if($rowCheck > 0)
{
while($row = mysql_fetch_array($result)){

// Start the login session

session_start();
$_SESSION['user'] = $_POST['user'];
$_SESSION['password'] = $_POST['password'];

header('refresh: 2;url=/client/'.$_SERVER["PHP_AUTH_USER"].'/clindx.php');
echo "Success! You will now be redirected.";
exit();
}
}
else {

//if nothing is returned by the query, unsuccessful login code goes here...
echo 'Incorrect login name or password. Please try again.';
}
}
?>