built-in camera for my macbook air stopped working

The built-in camera for my macbook stopped working and I tried following one of the suggestions I found on this platform by typing "sudo killall VDCAssistant" on the terminal app but instead of resolving the problem, the result I got was "No matching processes were found". Is there any other way I can resolve this?

I'm also having trouble installing the macOS High Sierra on my mac. I've downloaded the software on my laptop but every time I try to install it, the response I get is "The recovery server could not be contacted". Is there any way to fix this?