iMac not detecting Airport base station

Hi. I'm an oldy so apologies for technical ignorance! Internet comes into house through DSL and connects to a server (it's a ReQuest music server). From server, ethernet cable into Airport Extreme Base station. From base station, ethernet connects to iMac. I therefore connect to internet via the ethernet cable.

For the last 5 months up until today...the airport base station had a green light and other computers in range in my house could connect to it wirelessly. Now the amber light blinks. When I run Airport utility (ver 5.4.2) and it scans, it doesn't even "see" the airport base station and I can't even get into manual set up because it can't see any wireless device to set up.

Anyone come across this before? I have bought a Time Capsule and plugged that into the mains (within 20ft) and it doesn't even recognise ("see") that when it scans for a wireless device.

Any help much appreciated.

Thanks

G'day and welcome to the forums from one oldie to another!

What does Apple System Profiler in About this Mac > More Info.. > Airport have to say about the installed Airport Card? Not all machines came with Airport Cards installed as standard and they do fail alas.