Ethernet ports green lights dead or not activated?

There are fragments of answers to this questions in many other posts - but no step by step solutions that fit my configuration, and all attempts on my part to follow different solutions lose functionality and cause me to have to "reset to default" and use the partially functional settings.

GOAL: to use ALL the ethernet ports (3) on the Airport Extreme for additional devices.

This device is otherwise fully functional, with the main ethernet port just to the left of the WAN (circular icon) port providing all the "wired" services in our video production studio to the one main G5 Dual that does not have wireless, and uses it's Ethernet port to connect to the Airport Extreme -

the Airport Extreme is connected to an ATT Motorola Modem - which is set to bridge mode (as I have been instructed).

We have 3 other computers - all with wireless capabilities - that use the Airport Extreme wireless router to transfer files as well as access internet.

Question #1 - do you have to sent your modem internally to bridge mode AND set the Airport Extreme ALSO to bridge mode? Any time I attempt that, all Ethernet cables seem to "disconnect" and "Network" preferences all change from Green to Yellow.

Main Question: Why can't I get the remaining TWO ethernet ports to also work? I now have on-demand DirectTV and other devices that need an Ethernet option to work - and I thought I always had extra ports - but they seem dead - even changing all the cables around interchangably - the two left ethernet ports will not GO LIVE (turn green) when any cable is plugged into them.

Thank you so much in advance. Many hours spent trying every conceivable option - and instructions are confusing using terms such as "wireless" because I need the airport extreme to work "wired" and "wireless" as it has for over a year with 3 computers (one wired, 2 wireless) but trying to use the other 2 Ethernet ports is a dead end.