unexpected loss of Airport Extreme connection

My network: ethernet for all desktop Macs (old G5 tower, new Mini, 2009 iMac), two network printers (HP 5M, HP 7650 AIO inkjet) and an older Airport Extreme (spaceship version) mounted in the upstairs hallway ceiling for wireless access to an old Powerbook/iPhones/guest use. A Netgear switch in the attic is the main hub receiving all ethernet cables, then to the router and cable modem. The Airport cable from its WAN port goes to this switch as well.

This setup has worked perfectly for years and all ethernet still functions fine except for the recent loss of wireless connectivity to the Airport. I can no longer access via the Powerbook or occasionally connect by iPhone or Airport Express linked to the base station for music streaming to my audio system.

What I've tried:

1. checked ethernet cables to/from Airport with a circuit tester
2. both reset and unplugged the Airport base station, did a "fresh" setup by the Airport setup utility (no problem "seeing" the base station from any wired Mac)
3. the setup routine says "Success!" but no still no access from the Powerbook
4. checked the usual password/access control options, etc.
5. taken out and reseated the Airport card from the Powerbook
6. There is no specific error message when trying to connect via AIrport, just "cannot connect to this network)
7. reset the cable modem and router

So...

Is it likely that this is a problem within the Airport Extreme itself? It certainly seems that the basic network is working fine. It's at least five years old by now. Any other ideas welcomed!

KWO