Powerbook G4 that drops the internet connection

I need your thoughts please

Powerbook G4 15 " holds the internet connect for about 2 minutes, then drops it completely. Goes from full set of greens then loses them.

Checked: Airport, Firewalls, Preferences, and no joy. Tried deleting all preferred networks, but they come right back. Why ? How do I stop this? Do I need to? Disabling 'remember any network' will switch itself back on after a pause. Bizarre.

This is a 2004 model, that has had no problems up until now. We have not changed servers, internet access, passwords , in fact no change anywhere. WP running windows 7 has no problems, and has not changed anything either.

All help gratefully received, and thanks.

sounds like there is a problem with the airport card itself or the antenna connected to it. I had an iBook G4 a long time ago, and i could take it apart and access the airport card, but i do not remember if it was possible on a powerbook.