Does the brush rotate if you move them with your fingers? (Unplug first!)
If the brush moves very freely then the belt has snapped. This happens sometimes. Undo the base plate by turning the four yellow plastic clips and you'll see the broken belt and where a new one should go.
If the brush won't move at all then the bearings have gone or have been jammed, and quite possibly the belt has then gone. Undo the base plate as above and the brush should slide out. If you cannot then free or unjam the bearings you'll need a new brush and belt.
David Jones, May 2011
