Airport icon turned grey, no networks shown

Question

G4 Quicksilver running 10.4.11
Last night after several years trouble free operation Airport on my wife's G4 suddenly started cutting out and then coming back in. Sometimes it was off for a few seconds, sometimes for a few minutes. Restarting didn't cure the problem.
This morning it was steady for several hours, then started cutting out/in, now it seems to be mainly out.
What happens is this. The black airport icon turns to grey with all bars still showing and connection is lost. When this happens available networks were initially sometimes shown in the drop down menu, sometimes not (usually there are four or five neighbouring networks shown).
When networks are shown clicking on ours sometimes, but not always, brought it back on.
When no networks are shown going via ‘Other’ and entering our details initially brought it back but no longer.
At present the Airport icon is showing grey with four bars all the time.
I have tried reseating the Airport card and checking the aerial connection but these seem OK. (I’m assuming that the existence of four bars at all times shows that a signal is being received so card problems are unlikely; is that right?)
I have deleted com.apple.airport.preferences.plist
I have zapped PRAM and repaired permissions.
I booted from an external HD (10.4.2) and the same problems appeared. The fact that the same problem exists with another boot disk suggests to me that the problem lies in the G4 rather than software.
Any ideas, please?
(I started a similar thread in the G4 forum which has had no takers so far and as Tiger forums seems to get more Airport traffic I thought I would try here.)
Michael

Answer 1

+”Get Temperature Monitor - 4.51 to see if it's heat related”+
I’ve used Temperature Monitor in the past and it only shows drives, not CPUs on our G4s. (Reading round this seems to be a problem with the current version and I can’t find any earlier ones.) However I reinstalled TM and it showed drive temperatures going up and then staying very steady at around 35° for the boot drive (newer) and a bit lower for the original HD. I haven’t actually observed the CPU fan running but air is definitely moving through its vent. The CPU/fan area is clear of dust.
However I’m beginning to go off my temperature theory as the pattern of the problem has changed.
It originally started to show itself when the Mac had been in use for some hours and would then mean that Airport would not show any network virtually continuously until shutdown. Now at boot it may be OK for several hours, a few minutes or not at all. During the day it will sometimes come back for some hours or just minutes.
In all cases the symptoms are the same. The Airport icon turns grey but retains four bars. No networks are shown in the dropdown menu. Turning Airport off/on has no effect. Sometimes it will return on its own, sometimes networks are shown in the menu and connection is then usually possible.
I have now tried booting it from the backup HD I use for my G4 (10.4.11) and the problem as described was present from the outset. To be strictly accurate I booted it from its own startup disk and Airport was OK but when I restarted using the other drive via Startup Prefs Airport showed five grey bars but no networks.
I have also rebooted the router in case that was involved.
With my limited understanding of what makes Macs tick all this suggests that the problem must be within the G4 either in data (but PRAM has been zapped) or hardware rather than being a system issue.