Restore and backup >> Factory reset

I am facing a few connection issues regarding the software update and WiFi. So, I want to back up my data to my computer and the factory reset the device. The problem is that the iPhone does not show up on my iTuens even though I am signed in. Also, I could not sign to iTunes in my iPhone; it is not responding. I would really appreciate your prompt help to resolve this issue.

Many thanks,

Hatem