CodeIgniter Does not run Hello world

[eluser]codeman[/eluser]
hi Guys,

I started learning Code Igniter Today and i am not able to run hello world program,

SO i have Localhost, i installed apache and Mysql and everything, I tried running PHP code as well works fine,

So i did download codeigniter and put it in the localhost and try to create first controller like this....
<?php
class Blog extends Controller {

function index()
{
echo 'Hello World!';
}
}
?>

Now i go to the path http://IP/CodeIgniter/index.php/blog

and it does not print Hello world, What should i do?

What am i doing wrong?

Please help me