ช่วยดูให้หน่อยครับ $Oldusename มันไม่แสดงค่าครับมันยังเป็น =<?=$Oldusename?> อยู่เลยครับ

<?
session_start();
if(empty($username))
{ header('location:admin_form.php'); exit(); }
require_once("include/connect_db.php");
require_once("include/function.php");
require_once("include/check_data.php");
$con=connect_db("####"); //ติดต่อฐานข้อมูล
$sql="select * from admin where ID_ADMIN='$ID_ADMIN' ";
$result = mysql_query($sql);
$row = mysql_fetch_array($result,MYSQL_ASSOC);
$Oldusename = $ID_ADMIN
?>

<script language="javascript">
function fncSubmit()
{
	if(confirm('Are you sure ?')==true)
	{
		return true;
	}
	else
	{
		return false;
	}
}
</script>

<table align="center" width="500">
<form action="edit_admin.php" method="post" enctype="multipart/form-data" onSubmit="JavaScript:return fncSubmit();">
<tr>
<td bgcolor="#AACCCC"><font face="MS Sans serif"><b>USENAME</b></font><font face="Ms Sans serif"><b> : </b></font></td>
<td colspan="2" bgcolor="#DDEEEE"><input type="text" value="<?=$row["USENAME"]?>" name="USENAME" maxlength="60" size="40"> 
  <input type="hidden" name="ID_ADMIN" value="<?=$row["ID_ADMIN"]?>" /></td>
</tr>

<tr>
<td bgcolor="#AACCCC"><font face="MS Sans serif"><b>PASSWORD</b></font><font face="Ms Sans serif"><b> : </b></font></td>
<td bgcolor="#DDEEEE" colspan="2"><input type="password" value="<?=$row["PASSWORD"]?>" maxlength="100" size ="30" name="PASSWORD"></td>
</tr>

<tr><td align="center">
<input type="hidden" name="Oldusename" value="$Oldusename">
<input  type="submit" name="edit" value="edit username"></td>
</form>
<form action="delete_admin.php" method="post" onSubmit="JavaScript:return fncSubmit();">
<td align="center">
<input type="hidden" value="<?=$row["ID_ADMIN"]?>" name="ID_ADMIN">
<input  type="submit" name="delete" value="delete username "></td>
</form>
<form action="showdata_admin.php" method="post">
<td><input type="submit" name="Back" value="Back"></td>
</form>
</table>

<?
require_once("include/check_data.php");
require_once("include/connect_db.php");
require_once("include/function.php");
session_start();

if(!$USENAME or !$PASSWORD)  
{
header("location:edit_admin_form.php=<?php echo "$Oldusename" ?>");
exit();
}

$con=connect_db("####"); //ติดต่อฐานข้อมูล
$sql = "update admin set USENAME = '$USENAME' , PASSWORD = '$PASSWORD' where ID_ADMIN='$ID_ADMIN';"; //ตารางข้อมูล 
$result = mysql_query($sql);
if($result)
{
session_register("error");
$error = "Insert Design Successfully";
header("location:showdata_admin.php");
}
?>

header("location:edit_admin_form.php?ID_ADMIN=$Oldusename");