Shortcode no 'Thank You' response

I’m using the shortcode to call the form on my contact page, it works fine however when submitted the screen goes dark as though the modal ‘Thank You’ should pop up but nothing appears, then the screen goes back to being normal. Form gets submitted fine. Any idea how / why the ‘Thank You’ box is not appearing?

http://ww.wp.xz.cn/plugins/usernoise/