WiFi turns off for no reason?

Netgear FWG114P with latest firmware and almost all settings at defaults.

Ethernet clients work fine.

WiFi clients (3 different adapter types) work fine UNTIL the AP just stops
sending for no apparent reason. All 3 clients at the same time, after who
knows how long say there is no AP out there.

A reset or power-off reboot solves the problem for varying lengths of time,
from a few hours to a few days.

Why does the AP just suddenly stop sending??? More important, what can I do
about it?