Can't connect to Yahoo mail on one device

I'm connnected to Comcast and cannot access Yahoo Mail on my IPAQ PocketPC (running Windows Mobile 6 Classic OS on Wi-Fi). Other devices on the router can connect fine. I found that by connecting a second router to my main router using a cross-over cable, and then connecting the IPAQ to the second router via wi-fi, I can access Yahoo Mail fine on the IPAQ. (The second router here is factory-defaulted.)

I factory-defaulted the settings on the main router to see if I could get access -no luck. Connecting the second router directly to Comcast sets off a firestorm of activity as they have to recognize and initialize it and assign settings for their network. That's understandable. I'm aware that Comcast controls portions of my router remotely as a pre-condition for using their service. Is it possible that they have changed a setting (service, ports, etc.) that is preventing this access? I can call them for help as soon as I come up with an intelligent question <grin>. Any help will be appreciated...