A relatively common problem - they make the wires extra flexible and in doing so use very fine conductors - continual strain at the bending places - close to one end or another - eventually causes the conductors to break until they're all open circuit. You can cometimes find the point of failure by using you fingers at the likely places while you listen for an ear to suddenly start up for a second.
Repair, however, is not always possible and if you can manage to do it, it's seldom efffective in the long-term and never very pretty.
Peccavi
November 2009