Sessions problém - nezavedú sa

<?php
session_start();
if(isset($_POST['nick'])){
$url=$HTTP_REFERER;
$nick=$_POST['nick'];
$pass=$_POST['pass'];
$zakazane=array("<", ">");
$nick=str_replace($zakazane, "", $nick);
$pass=str_replace($zakazane, "", $pass);
$passMD5=md5($pass);
if($pass=="" || $nick==""){
header("Location: ".$url);
}else{
require_once "config.php";
@$connect = mysql_connect($host, $name, $pass) or die ("<span style=\"color: red\">Pripojenie k serveru <b>".$host."</b> zlyhalo.<br><b>MySQL Chyba:</b> ".mysql_error()."</span>");
mysql_select_db($db, $connect) or die ("<span style=\"color: red\">Pripojenie k databáze <b>".$db."</b> zlyhalo.<br><b>MySQL Chyba:</b> ".mysql_error()."</span>");
mysql_query("SET NAMES cp1250");
$kontrola=mysql_query("SELECT * FROM `users` WHERE `username`='$nick' and `password`='$pass'") or die (mysql_error());
$row=mysql_fetch_array($kontrola);
if($row['username']){
$_SESSION['logged']=1;
$_SESSION['nick']=$row['username'];
$_SESSION['id']=$row['id'];
$_SESSION['prava']=$row['prava'];
header("Location: ".$url);
}else{
header("Location: ".$url);
}
}
}
?>