I had the exact same problem, unfortunately I didn't fix this until today (2 years later) when my large brush roller stopped spinning on carpet and the green light would stay on. There are 2 screws that need to be tightened, one per roller head. For me, tightening those was enough. Some people recommend getting a new belt for the system but the belt was kind of hard to get for me. I also removed any stuck on lint or hair in both the rollers and the vacuum was working perfectly again!! If it doesn't work, contact Shark customer service, they could help you get a replacement motorized head for a lower price.