Hey!
This site seems to work fine: http://breitkopf.bplaced.net/
If you want to set up everything so that when you go to "www.motionbrandingmotionbranding.de" and it shows the contents of "http://breitkopf.bplaced.net/" but the domain name "www.motionbrandingmotionbranding.de" always stays in the url address bar; Theeen you need to update your database to not have "http://breitkopf.bplaced.net/" entires anymore, but just "www.motionbrandingmotionbranding.de" entries. So basically you need to replace the old url with the new one. The plugin "WP Migrate DB" helps with replacing urls and exporting your database. After that you'd need to replace your old database with that one. Make sure to have a backup!
I just wrote a little tutorial about all that here: http://laytheme.com/how-to-use.html#moving-website