I recently set up my modem/router through xfinity, and after activation I unplugged the Ethernet cord to try to connect my laptop to wifi. My phone is connected and working well but my laptop won't go online even though it's showing that it's connected to my network. I spent over an hour on the phone with Comcast troubleshooting, and we determined it has something to do with my computer. The computer was connecting to other networks just fine before I plugged in the Ethernet cable (it was the first time it ever had one plugged in) but now won't work on any wifi network including ones it had previously worked on. Help!!!
Boot the computer to Recovery (hold Command and R on restart) and ensure it connected to your WiFi network. Then select Get Help Online. This actually loads a file stored in Recovery, so type in a URL and see if it loads. If it does not, your computer is not the issue.