Strange. If the modem power is connected to a surge protector, connect direct to the wall outlet. Reboot the modem (it will reboot on resuming power when changing the outlet; otherwise remove and then restore the power adapter to reboot). Have a look at the modem information web page http://192.168.100.1 and post back the upstream and downstream power, signal to noise ratio, etc. You can consult the cable modem faq atfor additional information. You also might post to the Adelphia broadband forum for specific help. You should have the power information when posting there.
Do you directly connect, i.e., no router? What is your firewall and anti-virus (hopefully you have both)? If there is no router, do you reboot the modem before connecting the xbox?Q