I have one of these that has worked well for years, but has now
developed a bizarre problem. As soon as you put the battery in, it
switches on - without going anywhere near the power button. It then
boots fine, but if you press any button (apart from the power button
which does nothing) it then switches off again immediately. I've had
it apart and back together again with no sign of any change. I
thought that the power button might be stuck down - but have done all
I can think of to try and free it to no avail - it 'feels' as though
it's OK (you can feel the switch click down and back up again).

Any ideas? Any help gratefully received.