Can’t access the internet, home wi-fi is okay

Can't access the internet from my iMAC on my Wi-Fi. All other Apple hardware, iPad and iPhone function as they should. I took it to the store where I purchased it and a technician started it, connected it to their network and everything worked fine. Took it home connected it to my wi-fi and still had the problem.

This started at our previous house and xfinity installed all new equipment in our new house. I rebooted the gateway just to see…