Original post by: rdklinc ,
This is probably obvious, and it sounds like you know what you're doing, but make sure the connector is firmly plugged into the airport. Sometimes it feel like it's attached, but then if you apply more pressure you get another "click" when it goes all the way in, and that definitely affects reception. Other than that, if you're trying a known-good card, I'm not sure what would be the problem, because you've replaced all the hardware. Have you done a fresh install of the OS? I've seen machines with gunked-up VPN settings that had wireless problems until the network config was reset. Also, I've seen machines with 10.5.0, i.e. machines that were not patched to the latest OS revision that could not see the wireless card or otherwise had odd wireless issues.