Issues with Comcast and Airport

I signed up for Comcast internet and have had it for a few weeks now. I still cannot get my wireless to work. Comcast told me that they do not have support for Airport Extreme's, and since it's more than a year old, Apple will not help me. When I am connected directly to the modem with an ethernet cable, my internet works perfectly.

I have read many forums and tried everything, resetting both, leaving both unplugged for 15 minutes, turning one off and resetting that while leaving the other on, etc. Nothing has worked.

The Comcast guy tried to tell me that since my router was more than a year old it was "old". It is an Aiport Extreme 802.11n bought exactly a year ago. I really do not think age is the issue here.

The modem brand is a Scientific Atlanta 2100. I can set up a network just fine, but then I get a "no internet connection" error in the Airport menu bar at the top of my screen.

If anybody has any more hints or ideas I would greatly appreciate them!

Thanks so much!