ช่วยทีครับ คือว่าติดตรงที่ ทำยังไง pass กับ old pass ก็ไม่ตรงกันซักที

<?PHP
	session_start();
	if(!isset($_SESSION['username']))
	{
		echo "<script>alert('please log in ');window.location='index.php';</script>";
		exit();
	}
	include("connect.php");
	$username		= $_SESSION['username'];
	$oldpassword	= base64_encode($_POST['oldpassword']);
	$newpassword	= base64_encode($_POST['newpassword']);
	$renewpassword	= base64_encode($_POST['renewpassword']);
	
	if(empty($oldpassword)||empty($newpassword)||empty($renewpassword))
	{
		echo "<script>alert(' Please Refill form ');history.back();</script>";
		exit();
	}
	
	$sql 	= "select * from member where username='username'";
	$query 	= mysql_query($sql) or die ("error=$sql");
	$row	= mysql_fetch_array($query);
	
	/*if($row['password'] != $oldpassword)  
	{
		echo "<script>alert('please change oldpassword ');history.back();</script>";
		exit();		
	}*/
	
	if($newpassword != $renewpassword)
	{
		echo "<script>alert('please change newpassword ');history.back();</script>";
		exit();		
	}
	
	$sqlU = " update member set password='$newpassword' where username='$username'";
	mysql_query($sqlU) or die ("error=$sqlU");
	echo "<script>alert('change password complete');window.location='main.php';</script>";
?>