处理页面不工作

我正在为一家公司创建一个内部网，我已经完成了登录/处理页面，但它不能正常工作。我试过无数次修复它，让它工作，但我仍然不断只是得到一个空白页，当我运行它。我想知道如果它是调用重定向通过头部在结束…有人能告诉我我做错了什么吗?

这是我更新的代码:

<?php
session_start();
include_once "databaseconnect.php"; 
// username and password sent from form 
$myusername=$_POST['user']; 
$mypassword=$_POST['password'];
// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysqli_real_escape_string($myusername);
$mypassword = mysqli_real_escape_string($mypassword);

$result= mysqli_query($connect,"SELECT * FROM access WHERE user='$myusername' AND password='$mypassword' ");
// Mysql_num_row is counting table row
$count= mysqli_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){
    $row = mysqli_fetch_row($result);

    $_SESSION['username']=$row['user'];
    $_SESSION['password']=$row['password'];
    if($row['user']== $myusername)
    {
        header("location:dashboard.php");
    }
    else
    {
        echo "Error in Validating User";
    }
}
?>