Since upgrading to WordPress 3.6, one of the most annoying bugs is the fact that drop down/expanding menus no longer work. For example:
Boxes in the admin panel with the little arrow to expand/collapse such as the ‘Right Now’ box in the dashboard, does not work. This is also true for widgets and the ‘kitchen sink’ in articles where highlighting text to make a URL no longer works.
However, the biggest problem is within the Gravity Forms plugin. I can add fields, but ONLY the first one will expand, all the others stay closed. Moving them around also does NOT work.
Have you tried deactivating ALL plugins and switching to twentytwelve theme to start trying to identify where the problem may be? If the problem goes away, reverse the steps one by one to see which plugin (or theme) is causing the problem.