mtbrandall

try doing a tracert his will trace the route from your pc to your server. open CMD and type tracert yourdomain.com it should list a series of hops between you and your server if any appear as ** then this coud be causing the problem.

try just doing it in php and adding [code] <?php if(!isset($_GET['f'])){ //see if ?f is not set     header("Location: error404.php"); //send the user to the 404 page     exit(); //terminate the script } ?> [/code]

some ISPs block access to certain ports such as port 80 to prevent them being used for commercial purposes. if you get in contact with your ISP thy should be able to advise you on this and if they are not blocking port 80 they should be able to advise you on how to rectify the problem.