Unable to upload theme

Am having an issue uploading the theme I bought from you guys can someone assist i have read the documentation and still am having an issue. I was able to upload the Highend child theme but when I upload either the demo or theme files I am brought to a page that states my page isn’t working and didn’t send any data with ERR_EMPTY_RESPONSE and when I diagnose the errors it is “unable to ping gateway.” I’ve tried both at work and at home to upload the theme but am presented with the same message each time.

PLEASE HELP!