I have an airport extreme router that my iMac is connected directly to. I also have a macbook and PC laptop that I can connect to wireless. All 3 of these devices can see the external drive that is connected via usb to the Airport extreme.

However I also have an old PC desktop that like the IMac is connected directly to the router. It doesn't seem to be able to see the external drive.

Any help on this?

(I was able to get the PC laptop to see it by mapping the drive on the wireless network....the desktop is not connecting wirelessly)