Go Online - Real World Server - Index.php

Hello everybody,

I managed to complete my first project with Yii.
I tried to get online.
When i write mydomain_name.com i see the message:
"The server encountered an internal error." etc
My localhost/mydomain_name works without problems.

Do i have to change something in the index.php?
Such as

$yii=dirname(__FILE__).'../yii/framework/yii.php';
or
$config=dirname(__FILE__).'/protected/config/main.php';