hah sağolsun çözdüler sanırım. aşağıdaki cevap gelmiş
-------------------
The problem was the php directive at the .htaccess.
The server uses suPHP so the php directives should be used in a local php.ini instead of .htaccess.
I commented the line at the .htaccess and created a php.ini with the default_charset directive set as utf-8 in the same directory.

Everything should be working fine now.
The site is up again.