iMac g4 stopped seeing wifi networks

iMac g4 running 10.2.8. It had no problem seeing and connecting to my guest wifi network until a few days ago when it stopped seeing any networks at all. I rebooted the router and it was a fixed, or so I thought. I put the computer to sleep and when I woke it up later, the problem was back. Subsequent attempts to reboot the router did nothing. I tried creating a wifi network on the computer. Information on the screen reported that it was successful and the signal strength was at maximum, yet no other devices in the room could see the network. I removed the bottom plate and the airport card looked normal and connected, but I reseated it anyway, and still nothing. Could it be a bad airport card? Before I buy a new card, is there anything else I can try? I'm using ethernet for now, and that works fine, but I really would like to get the wifi fixed so I can eliminate the ethernet cable. I don't have the install discs so I can't run the hardware test.