Intermittant loss of internet

Hi,

My router sort-of starting losing it's connection to the internet.  By sort-of, I mean that I couldn't  use a browser or email on any of my devices.  However, I could ping google.com.

This started happening a couple of times a day and I finally determined that power off/power on cycling of my gateway (Netgear C3000) would fix it.  So, I thought that my gateway was the problem and purchased a new modem-only Arris SB6190.

When I connect the new Arris to the cable and then plug an ethernet cable from my computer to it,  I get the following settings on my computer:

IP address  - 73.108.236.140

Subnet mask - 255.255.252.0

Router - 73.108.236.1

DNS - 8.8.8.8, 8.8.8.4

These seem appropriate and the lights seem correct on the modem.  However, I can't go to xfinity.com/activate to activate the new modem.  The browser just times out.

So, how do I go about activating the new modem?

Thanks,

Bob