First off, unplug your vacuum, turn it over and remove the access plate. This is a large plastic plate on the underside of the vacuum’s base (you’ll need a Philips head screwdriver). Remove the five screws. Then, check the brush and belt for damage. If the brush appears damaged or won’t turn by hand, you can replace it by clicking here: http://www.bissell.com/15-brush-assembly-for-upright-vacuums-2031283?productid=98N4
If the belt is stretched or broken, you can order a new one here: http://www.bissell.com/replacement-belt-for-upright-vacuums-2031093?productid=98N4
If the brush still won’t turn, please take your vacuum to a technician. You can find your nearest BISSELL® Authorized Service Center by clicking http://www.bissell.com/support/product-support/service-centers/ or by calling 1-800-237-7691 and choosing option #1, available 24 hours a day.