Klassenproblem

[Katastrophe]

Hi,

also ich habe bisher folgende Klasse:

<?php
class Dent{

function Dent()
 {
  global $SERVERROOT;
  global $CLASSESROOT;

global $dbHost;
  global $dbUser;
  global $dbPassword;
  global $dbName;

require_once($CLASSESROOT."control/db/mysql4db.class.php");
  require_once($CLASSESROOT."design/libs/Smarty.class.php");

$smarty = new Smarty;   // Create template Object
  $db = new Mysql4db($create = "", $this->dbHost, $this->dbUser, $this->dbPassword, $this->dbName); // database object

//$this->dbUser = $dbUser;

$smarty->template_dir = $SERVERROOT.'smarty/templates/';
        $smarty->compile_dir = $SERVERROOT.'smarty/templates_c/';
        $smarty->config_dir = $SERVERRROT.'smarty/configs/';
        $smarty->cache_dir = $SERVERRROT.'smarty/cache/';
 }

function writeHeader()
 {
  $smarty->assign();
  $smarty->display('header.tpl');
 }

function writeTop()
 {
  $smarty->assign('aktuelles','Hier jibt et aktuelles');
        $smarty->display('top.tpl');
 }
}

?>

In einer anderen Datei steht:
<?php
include("config.inc.php");

require_once($CLASSESROOT."dent.class.php");
$dent = new Dent;
$dent->writeTop();

?>

Nun kommt folgende Fehlermeldung:
Fatal error: Call to a member function on a non-object in d:\dentona_new\classes\dent.class.php on line 38

WARUM NUR?

Danke