They have a rotating spindle in the centre and an interlock button to prevent operation unless all the pieces are assembled safely.
You do not say if the motor turns or not - if the problem is that the motor doesn't operate it will either be because the motor is defective (very unlikely) or because a piece of the lid is not operating the interlock - in which case get yourself a new lid.
You can test the motor by using a blunt pencil or something similar to activate the interlock switch - make sure the cutting blade is not fitted.
Good Luck..., September 2016
