How do you relace belt on A electrolux AP100 power head

the link to a video below shows belt replacement as well as brush, press the helpful button
Changing the Brush Assembly on an Electrolux Epic 6500 Vacuum Cleaner

You probably need a new belt,or maybe a hose.To take the nozzle apart there a screws at the bottom of the head.Take them out then just wiggle and gently pry to top off. Chris

if it is making a humming sound but not turning you belt is broken, if it is not check the reset switch (little res button) if that doesnt work check the connections between the cord of the powerhead and the wand, the wand and the hose, and the hose and the vacuum
give the hose itself a good look over sometimes the wires up by the grip break in the casing

manual > http://www.totalvac.com/manuals/electrolux_manual_Lux5000.pdf

The following is for most models of the Aerus Electrolux UR models.

Lay the vacuum on it's front so you can see the bottom of the powerhead as shown below. Befrore going further, hold your hand straight and move your hand across the opening for the brush. If the bristles don't make good contact, the brush also needs replaced.
Remove the four screws. Using a flathead screwdriver, place it into the two rectangle openings (shown with red arrows) near the wheels and gently pry on tab to release the top of the power head.



Flip machine over and gently lift back of cover which will release the front. Lift off and set aside.

This is what you should see. Remove the two screws at the ends of the brush. Check carefully how the ends of the brush fit in. Gently lift out brush. This is a good time to clean entire interior of the power head. Install new belt over motor shaft and teeth of brush: set brush into place. Insert screws. Check tension of the belt.

Replace cover of power head, being sure to settle front in just beneath the lip of the front of the base first. Press down until it "clicks" into place. Turn machine over and insert and tighten screws.

Lay the vacuum on it's front so you can see the bottom of the powerhead as shown below. Befrore going further, hold your hand straight and move your hand across the opening for the brush. If the bristles don't make good contact, the brush also needs replaced.
Remove the four screws. Using a flathead screwdriver, place it into the two rectangle openings (shown with red arrows) near the wheels and gently pry on tab to release the top of the power head.
Flip machine over and gently lift cover off and set aside.

This is what you should see. Remove the two screws at the ends of the brush. Check carefully how the ends of the brush fit in. Gently lift out brush. This is a good time to clean entire interior of the power head. Install new belt over motor shaft and teeth of brush: set brush into place. Insert screws. Check tension of the belt.
Replace cover of power head, being sure to settle front in just beneath the lip of the front of the base first. Press down until it "clicks" into place. Turn machine over and insert and tighten screws.
Your vacuum is now ready to use.

Have you tried pushing the reset button? I'd try that first. If that doesn't work it could be that the belt is broken. The motors don't go out very often on those.

Flip the power head upside down and look for 5 black screws recessed in the bottom of the head...2 mid way back and 3 along the brush area. Once removed the lid should lift off. Be careful not to disturb the wiring harness.
The brush roll has a pulley and bearing end. Both should be cleaned and any hair or thread removed. The motor screws will have tensioning positions for the new belt so leave enough slack so the new belt depresses slightly. You will find a replacement at vac shop or thru AERUS Electrolux dealers

You need to change the belt
http://evacuumstore.com/c-99-electrolux-belts.aspx?manufacturerfilterid=0