Slider Issues!

Hello.. My client’s intern was messing with their site and now their slider isn’t working. Could somebody please assist me? If so, I can give you more info. Here is the site.
http://lansinghousingproducts.com

I believe it is “WP Nivo Slider”. But when I add more “posts” using featured image for the sliding images, it only shows one image and won’t go to the others? It’s extremely annoying. Can anybody assist? I can send credentials to get into the site if you can assist! Thank you!!!!!

jasoncamino