ช่วยด้วยค่ะ login check ไม่ผ่าน ... Username หรือ Password ไม่ถูกต้อง ... error ตลอดเลยค่ะไม่แจ้งอะไรเลย

<?
$host="localhost";
$username="root";
$password="root";  
$db="dataemployee";
$conn  = mysql_connect($host, $username, $password) or die("can not connect Data base");
mysql_db_query($db,'set names tis620') die("can not select Database");
mysql_select_db($db,$conn);
?>

<?
session_start();

 if (isset($_POST['txtusername']) && isset($_POST['txtpassword']) && !empty($_POST['txtusername']) && !empty($_POST['txtpassword'])) 
  {
    //$host="localhost";
	//$username="root";
	//$password="root";  
	//$db="dataemployee";
	//$conn  = mysql_connect($host, $username, $password) or die("can not connect Data base");
	//mysql_db_query($db,'set names tis620') die("can not select Database");
	//mysql_select_db($db,$conn);
	 require_once('../connectdata.php');
    $sql = "select * from emp where (ename ='".$_POST['txtusername']."') AND (password ='".md5(trim($_POST['txtPassword']))."')";
                      

                $result = mysql_query($sql);
                $num=mysql_num_rows($result);
                $rs = mysql_fetch_array($result);
                if($num)

                  {  

                               $empno = $rs['empno'];
                                $ename = $rs['ename'];
                                $level = $rs['levelusing'];
  
                                session_register("empno");
                                session_register("ename");
                                session_register("level");

 
                    if($rs['levelusing']  == 'a')
                                   header("Location:menu_admin.php");
                                else
                                  header("Location:menuu_ser.php");
                  }     
                   else
                               echo "<script> alert(' Username หรือ Password ไม่ถูกต้อง ');  location = 'login.php' ; </script>";    
   } 
?>