A common problem on laptop and other adaptors and vacuum cleaners and headphones too is a broken wire inside the cable.
Continual tight coiling up or constant tugging gradually stretches the metal conductors which elongate, thin and eventually break apart. You can't see the fault.
Your problem may not be this. Look first to the voltage level on the adaptor's free socket if you have the ability to measure it.
Good luck...
Peccavi, April 2010
