If you've recently "enhanced" your site with goodies and some older items no longer work, go back into the admin, and one by one turn the recent additional to "deactivate." Then, go back to you site and test. Be sure to test your site in ALL major browsers: Chrome, IE, Firefox and Safari – especially Safari on mobile devices. Check with and without the www – that can make a difference when there is a conflict. I spent hours with a tried and true slideshow script. It worked in IE, Chrome with and without the www. but in FF, it only displayed WITH the www. Paths were perfect, code was updated. The script author tried to help. We were baffled. Then I remembered reading about conflicts in overlapping calls to scripts.
THAT WAS IT! One by one I turned them off. The culprit – WPMobile Pack plugin. Once I deactivated all was well with the slideshow. Sometimes we work too hard to fix something. Many times we just need to step backwards and retrace our steps as to the last time it worked properly.
Be picky before you "invite" plugins to reside on your site. Do you really need it or is it just cool? If you find you never use it, deactivate and remove them because your headers may still call to them.