What size for parallex background image

When I add an image to the parallex background image, nothing shows. Am I using the wrong size?

 

Hi,

Could you please provide us URL of your website along with some edited screenshots so that we can assist you ?
In case, if you are unable to create screenshot , then you can follow the link http://www.screenpresso.com/ which will help you to create screenshots easily.

Thanks & Regards!
Nitin Sharma
InkThemes.com