Not sure how helpful this will be, as I'm running a different piece of gear, plus it requires both troubleshooting + ISP assistance. I had a similar problem with my AirPort Extreme: AirPort Extreme saw the Arris, iBook saw the AirPort Extreme, but no internet connectivity.
- In my case, I needed to set the AirPort to DHCP in the AirPort Utility application.
- Power down the AirPort Extreme
- Power down the Arris. You achieve this by unplugging the Arris *and* removing the back-up battery.
- Wait a few moments.
- Insert the battery into the Arris.
- Plug in the Arris power supply.
- Wait for the Arris to go through the restart protocol; when all the lights on the front panel are solid green, the start-up is complete.
- Power up the AirPort Extreme; wait for the front panel light to go solid green.
As I was doing this, I had my ISP on the phone that confirmed complete connectivity of the signal path and ensured that I was online. While the Arris was powered down, my ISP also sent a "message" to the Arris; I don't know if this was a software update or what. I completed the AirPort set-uo through the Utility application, the AirPort restarted, and I was online.
Hope this helps.