Untitled

Warning: Cannot modify header information - headers already sent by ERROR [closed]
<?php

$username = $password = $token = $fName = "";

include_once 'header.php';

if (isset($_POST['username'])&& isset($_POST['password']))

    $username = sanitizeString($_POST['username']);
    $password = sanitizeString($_POST['password']); //set temporary username and password variables
    $token    = md5("$password");//encrypt temp password

                        if ($username != 'admin')
                        {
                        header("Location:summary.php");
                        }
                        elseif($username == 'admin')
                        {
                        header("Location:admin.php");
                        }
                        elseif($username == '')
                        {
                         header("Location:index.php");
                            }

 else die ("<body><div class='container'><p class='error'>Invalid username or password.</p></div></body>");

  if ($username == "" || $token == "")
    {
        echo "<body><div class='container'><p class='error'>Please enter your username and password</p></div></body>";
    }
    else
    {
        $query="SELECT * FROM members WHERE username='$username'AND password = '$token'";//look in table for username entered
        $result=mysql_query($query);
        if (!$result) die ("Database access failed: " . mysql_error());

            elseif (mysql_num_rows($result)> 0)
                {

                    $row= mysql_fetch_row($result);
                    $_SESSION['username'] = $username;//set session variables
                    $_SESSION['password'] = $token;

                    $fName = $row[0];
                }
}

?>

ob_start();

output_buffering = On