Popcorn popper isn't popping popcorn
If it heats up, your popcorn may be old and dried out. If it doesn't heat up and the stirring rod does not turn, check your power cord for defects. Procedure: plug in the popper (check both ends of the cord!), turn it on, and gently wiggle the cord right at the plug or where it goes into the popper, and watch the stirring rod to see if it moves. If it starts and stops as you wiggle the cord, you've found the break in the cord. Repair it or replace it (West Bend lists it online for $5) and be more careful with the cord in the future (never unplug by yanking on the wire, always pull on the plug itself).
If the stirring rod turns and there is no heat, the thermostat or thermal fuse is probably open. This can happen in some poppers if the air vents are blocked on the bottom. Remove the obstruction from the vents, let everything cool off, and try again. If it does not heat up from a cold start, there may be a blown thermal fuse inside. If you decide to replace the thermal fuse or thermostat, it MUST have the same temperature and current rating as the original.