Can not customise theme or edit page

Hello, I just installed wordpress 4.1 and was not able to access the customise area of any theme properly (to change the header, background, etc.). It just shows a grey window with the save and publish button. On the tab of my webbrowser it reads Customise: Loading…
Another problem is that I can not edit any page. I can create one and give it a title, but I can not write a single word in the content box.

I don’t know if these problemes are related to each other but maybe there is a connection.