Can't install plugins

Hi there
I’ve just downloaded Highend theme (2nd license) and I am having 2 issues:
1. When I try to install Layer Slider and Revolution Slider I get a message saying that the server where this page is located isn’t responding.
2. when I try to install Essential Grid plugin I am redirected to mtenvelopes.com.au. The wordpress site for mtenvelopes.com.au is under development and is located in a folder (dev) within the public_html folder