WordPress header and including with class

Help me I’m lost.

I need do somethink like this, but error 500 occured.

Meaning: I need include header and footer to my program.

Example:

index.php file:

class start {

public function __construct {

require("pathto/wordpress/wp-blog-header.php");
get_header();
include("page.php");
get_sidebar();
get_footer();

}

}

$go=new start;

page.php file:
<h2>OK</h2>

Question: What I do bad? Where is there problem?
I make changes in code and no solution.