I recently purchased an older model Airport Extreme on Ebay. Came in the original box and looks as though it was never used. I installed it on my G5 single processor which is equipped with an Airport Extreme card. I get my internet from Cox Communications in Tucson via a Scientific Atlanta modem. When I do a diagnostic, it shows everything related to the Airport is green. But, it doesn't work and I have no connection to the internet. What am I doing wrong? Any help would be greatly appreciated.