PHP简单的HTML DOM解析器返回空白

I'm trying to get HTML DOM to work with a website but no matter how much I alter it, it doesn't work. Everything's just blank. Here's the code:

<?php

include_once('simple_html_dom.php');
$target_url = "http://beyonce.com";
$html = new simple_html_dom();
$html->load_file($target_url);
foreach($html->find('div[class=header-wrapper]') as $post)
{
echo $post."<br />";
}
?>

Site: http://beyonce.com!