wampserver in window : CodeIgniter doesn't show my pages

[eluser]absfrm[/eluser]
Hi
I've just moved to CodeIgniter! In my windows I've installed wamp server and when i load the localhost/ci ,
The welcome_message.php will load success.
But , I've created a file named : site.php and have written on :

Code:

<?php

class Site extends Controller {

function index() {
  echo 'something';
}

}

Then , when I load the address : localhost/ci/index.php/site . It shows nothing in firefox and in other browser will get error : server not found

why?

Please help, I'm new in CodeIgniter and this is my first try
Thank you.