รยบกวนผู้รู้ช่วยบอกหน่อยเถอะคะ ต้อง แก้ไขยังไงให้ login เข้าได้อะคะ ไม่รู้จะแก้ยังไงแล้วอะคะ

<?php
$conn = mysql_connect("localhost", "root", "hornet");

if (!$conn) 
{
	echo mysql_error();
	exit();
}

$charset = "SET NAMES tis620";

mysql_query($charset);
mysql_query("USE bis");

$message	=	"";

if (isset($_POST['username'])) 
{
	$username	=	$_POST['username'];
	$password	=	$_POST['password'];
	
	$strsql		=	"SELECT ID,UserName,Password,GroupID,DepartmentID FROM user WHERE UserName='$username'" ;
	
	if ( $username == "" ) 
	{
		$message="กรุณาป้อนชื่อผู้ใช้";
	}
	else 
	{
		$rs	=	mysql_query($strsql);
		
		if( !$rs )
		{
			$rs_row = 0;
		}
		else 
		{
			$rs_row	=	mysql_num_rows($rs);
		
			if ( $rs_row > 0 )
			{
				if ( $username == mysql_result( $rs, 0, "UserName" ) and mysql_result( $rs, 0, "PassWord" ) == $password ) 
				{
					@session_start();
					
					$_SESSION['ID']			=	mysql_result($rs,0,"ID");
					$_SESSION['username']	=	$username;
					
					echo "window.open('show.php','bis','width=1024,height=700,scrollbars=yes,toolbar=no');";
					echo "window.close();";
					echo "</script>";
				}
				else 
				{
					$message="ชื่อหรือรหัสไม่ถูกต้อง";
				}
			}
		}
	}
}
?>