The brush won't rotate and the belt on the side access panel is running. I borrowed this machine from a friend and I'm not sure how to fix it.

Most uprights have several screws holding the panel on the underside of the vacuum. You need to turn the vacuum upside down and remove the screws and the panel. This will give you access to the brush and the belt..
Don't forget to make sure the vacuum is unplugged prior to doing this!! Hope this was of some help.

If the roller doesn't run, make sure the AC power wires are all connected to the bottom roller section.
If that looks ok then look inside to see if the roller is loose or off the motor.

there are two belts on the 1698 one for brushes one for pump check the link below
http://www.vacsite.com/en/bissell-parts-1/bissell-parts/1698-upright-deep-cleaner.html

Needs a new drive belt. Find the screws holding the bottom panel onto the floor section of the vac. take out those screws and you should see the motor and the brushes and a broken belt underneath the panel. Check that the brushes spin freely. If not you may have something like hair or string or something jamming the brush. If so cut out the obstruction and then rotate the brushes again and look to see if they rotate evenly, without wobbling because in some vacs if the brushes become jammed and run like that for a while sometimes it wears out the bearings or bushings holding the brush in place and if they are worn you need to replace those as well or when you replace the belt and run the vac it wont take long to break the belt again.

There is a reset button on the side of the brush bar head. Press it.

Always make sure your machine is unplugged from the outlet before replacing the belt.
Newer Oreck uprights have an access plate on the right hand side of the base (as you're looking at it from the front). Remove the one screw from the access plate and slide it forward. Snake the new belt around the brush roll pulley and then strrrrrrretch it back to the motor shaft. Replace the access plate.
If your model does not have an access plate; turn the machine upside down, Remove all screws. Lift the bottom plate off. Observe the position of the brush roll ends, One side of each end cap will have several notches cut into it,this is the 'new' side, the other side is smooth, this is the 'old' side. You can reposition the brush roll the the 'old' side if your bristles appear worn down.
With the brush roll still removed; place one end of the belt over the motor shaft first, place the other side of the belt around the brush roll pulley and stretch the brush roll forward until it is back in place.
Spin the brush roll by hand before replacing the cover to ensure the belt is not pinched.
Replace to cover.

OK - there are two obvious things to check: 1. Make sure the brush is rotating. The DC14 has a 'brush control system" operated by a knob on the base in front of the right side wheel. Make sure this hasn't accidentally been moved to the "off" position. With it in the "on" position, switch the machine on, tilt the handle back and check that the brush roll is rotating. If it isn't, then there's a broken belt or a problem with the clutch mechanism in the brush control system. 2. If the brush is rotating, switch the machine off (and unplug it), turn it over and you will see a short length of clear plastic hose with spiral reinforcing that runs from the brush area to the motor. That hose often develops a split (which lets air in and reduces suction around the brush). Take that hose off (pull it off from the motor end and then unscrew it from the brush end) and inspect it carefully for any damage. If it is damaged, get a new one - don't try and repair the old one, it's not worth it.
I hope this helps - if so, please remember to rate my response. If you need more help, just post a reply here and I'll see what more I can do. Good luck!

Lift the headlight and rotate the thumb dial to release the carpet head. It will spin to the side. Rotate the square handle at the front of the vac fully to the left.
Remove the carpet head and open it from the bottom side. Observe which side had a little block below the LED belt indicator when you rotate the brush. The brush must go back in this way. The blocks at the end of the brush are color coded for height adjustment. Remove the brush, slide a genuine belt onto the center and close the bottom cover of the housing. make sure the brush spins freely, now look into the belt opening, round hole at the side. Using the square dial at the front of the head, rotate the hook into the belt to twist the belt and open it for installation onto the motor shaft.
Reinstall the head onto the vac, using the thumb dial to lock into place and rotate the square handle again . This will release the belt tension onto the motor shaft. Raise the vac up two knotches with the pedal before lower onto the carpet.

Hey there bankshots, if you look at the bottom of the head of the vacuum, you should be able to see the brushes. Their are some screws to remove to gain access to the inside of the bottom panel. When opened, you should be able to see the entire spinning brush assembly. On one side, there is an area which has no brushes and may contain the remnents of your belt which most likely is the problem. These belts are often replaced and not the sign of any thing to worry about. Replacements can be found at registered repair facilities. Alternately, a professional will do it for you for a modest charge. Also your warranty may cover this if your machine is less than a year old, or you purchased the extra protection from the seller. Good Luck!

Make the machine safe from the power source first
When you remove the belt access door you are looking at the pump belt,
To gain access to the brush belt you must turn the machine over and remove the brush at the bottom of the machine.
there are two screw in the red retainers at each side of the brush, remove the screws and the retainers and the pivot arms ,you should see the brush belt and the pump