disconnect the mains before starting any work on your machine
take off the back panel
be careful it's sharp on the edges
next look for the toothed gear on the small motor
it changes the drums to contrarotator mode
check if the rack it meshes with can be moved by hand easily
if so push the rack to the left fully till it stops
then try to turn the drum pulley
if this works then you may need more advice from the dyson helpline to diagnose the cause
hope this helps
chris
June 2008