I'd have to know a wee bit more. Such as the model/make of the Comcast MTA (or modem as you may call this black box.)
Comcast hooked up a new cable modem for me today now I cant get online using my apple airport base station. I can go online if I use ethernet from the modem to my imac. I dont know if there is a setting in my airport that is looking for my old cable modem. Noone seems to have an answer. any help?