my wk767 wont turn by itself?

The wk767 tumble dryer wont operate unless i spin the drum myself. I open the door and trigger the micro switch with a screwdriver and the dryer makes a noise of it sucking water and heating but no drum movement.
If i spin the drum by hand it then kicks into motion. any idea on whats faulty? either a switch near the drum or some sort of drum starter motor?

please help.

thanks