Diagnosis
The issue is with the food processor work bowl attachment, not the base. The bowl is not properly locked onto its base, or the lid is not aligned.
How to Fix It
Set the work bowl onto its motor base. Turn it clockwise until it clicks and locks into place. Place the lid on the bowl. The handle must be aligned with the 'Lock' symbol on the bowl. Turn the lid clockwise until the handle is over the 'Unlock' symbol. You should hear the motor engage when you press a button.
If That Didn't Work
Check the small plastic drive adapter that fits into the work bowl base. Ensure it is inserted correctly and not cracked. If damaged, the motor spindle won't engage. Part number is usually BFP-703-ADR.
Heads Up
The base has separate sensors for the blender jar and food processor bowl. If one works, the base motor is fine. The problem is always in the attachment assembly or its lock.