A 500 error just means that there is something wrong with the application server. You will need to enable full or advanced error reporting to see the error itself, this should be an option for your server.
If you do this and get a blank page it would indicate a php error is occurring, if that is the case you would need to enable error reporting to see what the problem is. You can do that with this code at the top of your page:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>