I just picked up a new modem, the Motorola SB5101, installed the software that came with it and when I go to connect to the internet I am instantly redirected to the comcast link to download the install wizard, after having downloaded it and started it, it claims I have no network adapter installed.
You only need to install the disk if your hooking up your cable modem via USB, the disk contains the drivers for the modem ONLY when you have it hooked up via USB. As long as you have a eithernet port, there is nothing to install, if your replacing the modem you have to call comcast and let them provision the modem, they will run you through the required steps to get you up and running.
In most market areas they changed to the new Bedrock system years ago where you will now see what is called the "Walled Garden" modem registration page in the browser when connecting an un-provisioned modem to the system. I believe that they would prefer that subscribers use this automated system over calling in so as to reduce their tech support operating expenses, but many people would rather not load any CC software on to their machines so they call in instead.
I have only been able to get the 'automated system' from the "Walled Garden" to provision a modem to work only once and thats the Scientific Antlanta 2100 Modem I have how now, its never worked with any other modem for me, I have always had to call in up until I got this modem.
Actually when it worked for this modem, it didnt replace my old modem, it added a second modem to my account, I remember getting the bill and was like what the heck, my account had 2 modems activated on it, had to call and have it removed and credited. It worked...... But never replaced the old modem. And yes I choose Existing Customer and not New Customer.