Be sure you are using only genuine BISSELL replacement belts. Belts not made by BISSELL may cause belts to break continually. If you need replacement belts, click on this link to order:
Adjust height of vacuum using the height adjustment knob. By raising the base slightly, this should help to ensure the brush is rotating freely.
If problem persists, please take the machine to a BISSELL Authorized Service Center to have a technician check it.
You can locate one by clicking here: http://www.bissell.com/support/product-support/service-centers/.