Or just alter your script, e.g.
PHP Code:
<?php
error_reporting(E_ALL);
ini_set('display_errors',1);
session_start();
...
Better yet is to set 'log_errors' and 'error_log' in your php.ini to log everything from every script. This is what you'll want to do eventually anyway.
It may be you have a fatal error, some sort of syntax problem that is causing PHP to not parse the page at all.
Is there anything revealed in the 'view source' option of your browser? Any HTML code shown? Or just a blank page?