Replace your belt by removing the screws from the baseplate, removing the baseplate and brushroll, and hooking the belt around the silver metal motor pulley. Then put the belt on the pulley side of the brushroll, and pull the brushroll back into its home in the front nozzle, ensuring that the brushroll ends are oriented the same direction. Spin it to ensure that everything spins freely, and then replace the baseplate. Party.

-R

Make sure that the wheels are not bound up with hair and thread and change the belt.
If you have deep shag or frieze carpeting then this is the best it will get.