I would want to start with a clean slate on the AirPort before connecting it. Also many will have connected a PC to the TM502G and that creates a problem. The MAC ADDRESS (which I will not define what that is since you can use google.com) is then locked onto and if you don't power cycle the TM502G it will not work with any other PC or router!

The reset of the Air Port is likely since DSL modems need a PPPoE login system...

Bob