I too have run into this problem with kitchenaid's food processor... I now use the Hamilton Beach 10-Cup Food Processor and could not be happier! I would recommend buying this processor for sure. Goodluck!

The fault can be with the power cord, the switch the motor brushes or the motor winding.

You need to open and check from the power cord , the continuity to the switch and to the motor. There is a safety switch in case the lid is not fixed into correctly as this will not run the motor. Also check for any rest switch in case of a power issue or overload which can trip the motor.

Your question did not mention any observation in detail. I suggest you to read this and you have got an idea: https://www.robotance.com/roboti...essor/processor-reviews/

Examine the work bowl and the lid of the KitchenAid food processor to determine whether they are locked into place properly. The machine will not turn on if either component is too loose or jammed into place incorrectly.

At first you can check the below process
1. Locked Motor

Signal lights aglow will indicate a locked motor if the speed light remains on and the Off/Pulse light is flashing. To reset the motor, press the Off/Pulse button.
2. Upside-Down Disc Blade
Shredding and slicing discs can mistakenly be assembled upside-down. Assemble a disc blade so the raised edge of the blade faces upward. To secure the disc, align the centre opening of the disc over the metal pin on the stem and fit the disc into the ridge of the stem.
3. Mispositioned Disc Blade
Properly assembled, the shredding and slicing disc blades should be located near the top of the food processor’s lid. This placement lets you push food through a feed tube directly onto the spinning disc blade. If the blade is too low, it will not work because there will be a gap between the incoming food and the spinning blade.
4. Jammed Food Stops Blade
Food caught in either the disc blade or multipurpose blade could stop the blades from spinning. Turn off and unplug the food processor before any attempt to dislodge jammed food.
5. Inappropriately Sized Food
Food chunks that are too large to be processed can stop the blades from turning, and if forced, will potentially damage the food processor.
Gently feed large foods like cheese blocks, carrots, and zucchini through the feed tube when using the slice and shredding disc blades. Never feed by hand. Always push food through the feed tube by using the provided pusher.
Place coarsely chopped foods into the bowl with the multipurpose blade, then press and release either the Pulse, Chop, or Purée button repeatedly for short spurts to break down chunks prior to finely processing.
After checking all of this if you problem is not solved then you should contact with a professional.

I also faced this same kind of problem and I immediately bought a new food processor. So I would like to suggest you buy a new one.