The brush is activated by the suction of the vacuum. If it stops spinning, that means that either there is a broken part inside housing that surrounds the brush, thereby lessening the power of the suction to spin the brush, OR there is a lot of debris, usually hair, trapped and tangled around the brush. That can cause a troubling amount of friction and cause it to stop spinning. Either way, you will need an Allen wrench set to open up the trigger head. I found this video on youtube which details how to do that. It's not my video, but it is helpful. https://www.youtube.com/watch?v=FwNDO3pUxzM
Nine years later, and this page was a godsend! However, the price of a new turbine simply wasn't cost effective, so I opened up the turbine and found a rusted, seized bearing. Don't let the idea of fixing the turbine scare you... it's not difficult at all if you know how to use a Phillips screwdriver. And if it's not working now, you aren't going to make things worse.
A bit of Internet searching will show you how to open the turbine, but even without a set of instructions, don't be afraid to take out those four screws. I was fortunate: I pulled that rusted bearing and went to Akron (Ohio) Bearing and showed them the old one. In 30 seconds the guy behind the counter handed me the identical bearing. I cleaned up all the plastic gears in the turbine, regreased them, and had it back together in no time. You don't live in Akron, Ohio?? - Just look for a bearing business in a city near you.
Have you tried resetting the machine using the reset button on the back of the vacuum? If not please press the reset button. Here are additional troubleshooting steps that you may apply to determine what's wrong with it.
1. Ensure that the power cord is firmly in. You may also try to unplug and replug the power cord.
2. This vacuums are equipped with a thermal motor protection circuit that will shut the vacuum down if it detects excessive heat up. Overloading due to a clog, or the bag being full can cause heat up.
3. Check the hose pipe or the upright's mouth and remove any obstacles. Use a broom handle to poke any debris that may become trapped in the hose.
4. Unplug the machine and use your fingers to pull out any debris in the machine's mouth. Cut any thread or string that may have become wound around the rollers. Plug the machine back in and press the reset button on the back of the vacuum.
5. Switch the carpet switch to the "Carpet" position if you are using the vacuum on carpet and the vacuum won't pick up debris. Turn the tool activation switch to the "Off" position. Take a look at the light marked "Brushroll." If it's illuminated, remove the cause of the jam at the brushroll.
6. If the vacuum allows dust to escape, check if all the covers are tight. The filters and vacuum bag must be installed correctly. The filters snap into place and cannot be washed and re-used. Make sure the base of the bag collar is on the bag supports.
Thanks for making contact and I'm sorry you're having difficulty.
I would suggest that this is a blockage of some kind as the pulsating is caused by a lack of airflow (the motor is protecting itself by pulsating and then ultimately cutting out).
I would recommend looking at the following video which will take you through a methodical way of checking this. The model in the video is a DC59 but applies to most cordless models: https://www.youtube.com/watch?v=fdnu4yk-5vI
Furthermore, I would check the bin inlet to make sure that the one-way door/flap is not jammed as this also can cause the problem.
If you continue to have difficulty, please give the Dyson Helpline a call on 1-866-693-9766 (US), 1-877-397-6622 (CA), 0800 298 0298 (UK). Our experts will be happy to talk you through some further diagnostic checks when you have your machine easily to hand.