My wifi has gone. No device I have displays the SSID. WiFi light is on, it is configured correctly... but the SSID simply does not display.

I used to be able to do a hardware reset and reconfigure everything to get the WiFi back. Now, not even the harware reset works. The WiFi is completely gone. I've done everything I can think of; changed WiFi name, changed password and security, changed channel, changed encryption... nothing works. 

The Wifi sometimes, but not always, briefly reappears with its default name after a hardware reset.

This is something that has only just started happening, I've had the MR6400 for maybe 4 few years now.