Hello mlreyes and welcome,
Please share the following information:
1. Are you using a Comcast SMCD3GNV? If not what Comcast Gateway are you using?
2. If you are using the SMCD3GNV, is your computer directly connected to one of the Lanports 1-4? If so, you should definitely be able to login to 10.0.0.1 , username=admin, password=password (if default). If you are using another Business Class Gateway, then try same interconnect using 10.1.10.1, username=cusadmin, password=highspeed.
Hope this helps you out.