Firstly, on "all floors" models, the brush-bar doesn't turn when the machine is upright; only when it is tilted back in the "use" position.
Most people who complain of this have simply turned off the brush bar (yes, they turn off). With the machine upright, standing on the left side of it, turn the round clutch control knob clockwise to the "auto" position and see if it works now when tilted back.
If not, you need to check the clutch unit next. Take the cover off and check BOTH belts are connected as they should be.
Your answer will lie in one of the above.
Manchester Vacs Dyson Parts, June 2010
