Fix-ya My Motorized brush bar is not turning.

SOURCE: motorized brush bar not turning on Dyson Vacuum

Apparent common failure is that either the thin yellow and or blue motor drive wires that run from the LH side of the vacuum where the "control board" is located down into the hinge / ball area become stretched and then fray and eventually break. Happened to my Dyson twice. First repaired under warranty, second took about 20 minutes. You need a Torx screwdriver to remove the LH panel ( 4 screws) and also an access panel (2 screws) at the side of the ball which permits access to the blue / yellow wire connectors. I replaced with a new wire and connectors having fed the wires through the access hole making sure sure enough wire was available for the movement of the handle. Also ensure that when the covers are replaced they do not trap any wires underneath.

SOURCE: Bought clearance item Sunday just found out the

This appears to be a loose connection. The below post was answered by highntools a while ago. It probably is related to you problem. That is why moving it back and forth makes it go on.
I have finally fixed my sister's dyson dc 15 beater bar problem. It was just 2 tiny broken wires connect to circuit board lead to the beater bar. The wires broke where they go through the black rubber gommet. You need a torx screwdriver tx 15 to remove 2 plastic covers to access the wires. When looking at the front of the vacuum, the gray covers located on the right side of the vacuum. 1 big cover with a black rubber gasket and other small gray cover is on the rotating ball area.

There have been several people who reported loose or burnt wires to be the culprit for the brush bar not working. The DC15 does not use a belt, but a motor that is control by the circuit board. And I really believe that in your instance, the problem is a loose wire between the circuit board and the brush motor.