If your cables are correctly connected turn in your cable modem. Then turn to the computer system that is connected to the cable modem. After this open the browser onto your personal computer that's connected to the cable modem, then refresh the display and visit the site. This brings your browser to the registration page, and then follow all of the documentation on the registration page, to enroll your modem. If the activation page doesn't open then visit xfinity.com/authorize to activate your modem. Then follow all of the instruction and provide your Comcast account number and phone number linked to the account. But when the page doesn't appear then delete the default/ present DNS server on your pc, then access Comcast activation page again.
xfinity.com/authorize
