Nothing works anymore

Hello,
we were trying to customize our webpage,by adding a few lines of Code in the function.php.after that the website was not working anymore.When i tried to go back to the editor to erase the code.I could not get into the administration area. And now when i try to open the administration area I only get a blank page. I have really no idea,what happended so if someone can make any suggestions, I would be very grateful. the website is http://www.dev.landesfilmdienst-thueringen.de