@Pkluong  Thanks for your message. With higher-pile carpet -  essentially what happens, the cleanerhead can end up creating an air-tight seal with the flooring and seizing up the brush bar/suction.
For these areas, you can try using the hand or non-motorized tools on those rugs/carpets. And also try the lowest suction mode here. 

Hi

i also had the same problem. Purchased the same cordless vac from Costco. 

It sounds like we both have the same type of carpet. 
I contacted Dyson support and they were very helpful. While on the phone I let them listen to how it just stopped working after a few seconds I can’t imagine being on my hands and knees vacuuming all the carpet and told the rep that. 
Due to it being brand new out of the box, they are sending me a new one.  I was very happy with the customer service rep as well. 
 

I hope this helps. There is nothing more disappointing than being so excited and finding out that the power head doesn’t work!

I have the same issue. Just purchased the V15 from QVC. Bar on the motorized head doesn't turn on carpet. Lot of money paid for this to happen. What gives?

I hope your warranty covered a new motorized head. I received a replacement tonight and fingers crossed it works tomorrow!  The Dyson support person I spoke to on the phone made me feel better about putting the details on my file. I’m hoping there are no other issues!  I’ve been doing my research about which Cordless vacuum I wanted and spent months and hours before finally choosing this one. 
 

I hope you’re given a good solution for yours that you’re happy with. And… I hope this isn’t an ongoing issue!