You don't say what's not turning. Is the motor and fan going round or is the motor just stopped and humming? If it is just humming and there is no clothes trapped between the drum and the rim, best call a service engineer. If the fan and motor are going around but the drum isn't, usually the belt just needs replacing. It could have snapped though because of a jammed drum, possibly caused by the drum bearings, usually on the back, being warn through.
Freddo
February 2009