My xbox wont connect to the internet!!?

i have scientific atlanta or something modem and a 50 foot ethernet cord to my xbox. on xbox.com it says xbox live is up and running but when ever i try to sign in, it tests the connection and it fails. when i test it again it completes the network part then the internet part is where it stops. i have my IP adress and the DDS or whatever in good. i just dont know whats going on. ive unplugged my router multiple times its annoying. dont answer this saying me too! or something. that doesnt help.