Test the lid switch. Located inside the machine next to the door, a defective lid switch may prevent the machine from functioning at all. Make sure the plastic tab that pushes the lid switch is intact and aligned with the switch. Test the switch by pressing and releasing. It should click every time you do this. If either the switch or the plastic tab are broken, they will need to be replaced.
Check the spin cycle. If the washer spins, then the motor is functioning and the problem lies elsewhere. Check the belts. Tighten any loose belts, and replace worn or broken belts with new belts from Whirlpool.
If the motor and belts are spinning, the motor coupling may be damaged. This is a small plastic and rubber piece used in most Whirlpool washers, mounted to both the motor and transmission. If this has worn out, it will need to be replaced.
The electro-mechanical shifter in old Whirlpool models will prevent your washer from functioning if worn or defective. On newer models, other internal problems could be to blame. If the transmission is not functioning, call a Whirlpool technician.
If the transmission rotates but the agitator does not catch on the transmission shaft, examine the transmission spline for wear. When stripped, this prevents the agitator from properly gripping the transmission shaft. The spline or the agitator itself may need to be replaced.