The bristles will not spin. - Bissell 3522 PowerForce Bagged Upright Vacuum

Turn the vacuum over with the bristles up. Turn on the vacuum and see if the bristles are turning. If not, then replace the belt that makes the bristles spin.

Yes.

Belt can reamin intact but still jam and burn. It won't necessarily break. I suggest you remove the bottom of the vacuum where the bristles spins and where the belt is located. You may have something jammed in there. You may need to remove the bristle to get the belt out. Inspect the belt and replace after clearing the obstruiction.

Check to see that the belt has not slipped off of the bristle bar. If it smells hot that typically comes from the smell the belt makes if it is slipping. It will slip if it is not able to turn the bristle bar. Disassemble the bristle bar from the chassis and check the ends of it too see if they spin freely. It's typical that the ends get tied up with carpet threads and hair. Remove that mess, and then use some lubricant like silicone or Crisco cooking oil on the dowel of each end that is holding the bracket you had to unsnap from the chassis to remove the bristle bar.

Worn bristles are a fact of life for all vacuums with a brush roll. Where I work, we're changing them all the time! I don't think anyone has yet invented perpetual bristles. Sorry, but you'll have to fit a new one.

If still under warranty, take advantage. The brush roller may have bound-up bearings on the ends--usually string, thread, and hair are the problem. Check the drive belt for wear or damage. Hope this helps!

This suggests that the bristles on your brush roller are worn out.  When the bristles are a good working length, rotation of the roller actually helps to pull the machine over the carpet. When the bristles wear down this effect is lost.

no it can't be bypassed the motor is dc.the circuit board converts it from ac to dc

You may either have something caught up in the under part of the vacuum or the belt may be broken or partially broken causing it to smell like that. Try laying the vacuum flat on its back and plugging it up. Then turn it on and see if the brushes spin and if they do not, then you will need a new belt which is not expensive. Then check the bristles and the thing that holds up the bristles to see it there are any strings caught in them causing it to smell of burning. Take the strings out and then try it. It should stop smelling of burning.

check you belt to make sure it has not come off the brush or the motor.