[I know that this question is many years old but am adding an answer for the benefit of others!]
If the machine is tumbling, then it is to do with the heating element. If you remove the back panel of the machine (having isolated the supply obviously!), you will see the heating elements, with a couple of (fire? smoke?) sensors above it. Behind one of the sensors is a small red reset button. If you press this, it should click and reset the heating element.
Christof
October 2008