There are a few reasons this may be happening. The vacuum might not be set at the proper height. If the nozzle is too high off the floor, the brush will not reach the floor to clean it properly. To adjust the height, simply press the toe touch pedal on the side of the unit.
Another reason may be because the brush roll is not turning. If the brush roll indicator light on the nozzle is not on, that could mean the following: the brush roll isn’t turning freely or the belt is slipping, broken or not engaged. To engage the brush roll, flip out the belt lifter handle and turn it clockwise until the green arrows line up.
Lastly, you might have a full bag. Check the disposable filter bag to see if it’s full and replace it if it is.