Mac Osx 10.6.8 / sony blu-ray internet problem Xfinity. Connects to network but internet fail.

Alright, here's to hoping someone can help! I have the xfinity router/gateway integrated device (little tower) and up until yesterday all of my many devices worked seamlessly and able to get online. I in fact purchased a new MacBook Pro (only thing new that connected to internet though probably unrelated) yesterday and set it all up. It runs mavericks and works beautifully. The older MacBook Pro from 2009 running snow leopard began having connection issues. At first just dropping wifi. Then in the afternoon was only able to connect via Ethernet cord. I tried restarting and removing caches and files and attempted to reinstall the os. Nothing got it online.

It sees and connects to the 2.4gh(or ghz I forget.. But the 5 too) band BUT when running network diagnostics indicates the internet has failed. After several hours on the phone with Comcast trying every possible security level on the wifi, even open network, it still didn't work. Then I was feeling very defeated and tried to use my sony 3d blu ray player to watch some Netflix. It too has issues with the 2.4 network connection (this can't see the 5) and represented ALL of the same symptoms. Not connecting via Ethernet or open wifi. I'm losing my mind.

Does anyone know what I should try doing? Other than router settings Comcast reset my modem several times and like said the newer devices in the house (MacBook Air. MacBook Pro, desktop windows, kindles and smartphones) ALL Connect.

I read using the tower as strictly a modem and getting a separate router *might* help but I'm skeptical. Please help!!