Try adjusting the height of your vacuum using the height adjustment knob. By raising the base slightly, this should help to ensure the brush is rotating freely. To replace your belt, click here: http://www.bissell.com/parts/?sc=part&productid=2432&partid=4680
If the problem persists, please take your vacuum to a technician. You can find your nearest BISSELL® Authorized Service Center by clicking http://www.bissell.com/service-centers/ or by calling 1-800-263-2535, available 24 hours a day.