子宫脱垂 熏洗方:PHP 代码错在哪

<?php
session_start(); $user_name=$_POST["user_name"];
session_register("user_name"); require_once("sys_conf.inc"); $link_id=mysql_connect($DBHOST,$DBUSER,$DBPWD); mysql_select_db($DBNAME);
$str="select user_name,password from user where user_name ='$user_name'";
$result=mysql_query($str,$link_id);
$rows=mysql_num_rows($result);
$password=$_POST["password"];
if($rows!=0)
{
list($name,$password)=mysql_fetch_row($result);
if ($user_name==$_POST["user_name"])
{
if ($password==$_POST["password"])
{
$str="update user set online =1 where user_name ='$user_name' and password='$password'";
$result=mysql_query($str, $link_id); require("head.html"); }
else
{
echo "<script LANGUAGE='javascript'>alert('请输入用户名！');history.go(-1);</script>";
require("login.php");
}
}
mysql_close($link_id);
?>

无法运行 答对加分，sys_conf.inc是数据库配置信息，没有错
如果我把if ($password==$_POST["password"]){ 删除，那么输入用户名正确的话可以转到指定页面，输错的话一片空白，如果不删，那么出现
Parse error: parse error in C:\AppServ\www\test\ch_user.php on line 36