So if anybody has an idea how to solve it I would be very happy if you want to share it with me. Also about the image slider. It disappears on IE 7 - 8.
Drop the script tags in the <head> of your HTML. For best performance, you should have them follow after your stylesheet references. The reason we recommend placing Modernizr in the head is two-fold: the HTML5 Shiv (that enables HTML5 elements in IE) must execute before the <body>, and if you’re using any of the CSS classes that Modernizr adds, you’ll want to prevent a FOUC.