Inspect the washer agitator
The washer agitator is the large plastic piece at the center of the drum of a top-loading washer. As it agitates back and forth, it moves the clothes and helps the detergent do its work. Check to see if the agitator is damaged or broken. If the top of the agitator doesn't ratchet back and forth properly, its inner teeth may be broken. Replace the agitator if needed.
Check the agitator dogs
The agitator dogs are small plastic washer parts that control the movement of the agitator. If you notice that the top of the agitator is spinning freely rather than ratcheting back and forth as it should, the problem probably lies with the agitator dogs, which need to be replaced.
Check the washer drive belt
In some washing machines, a drive belt transmits the motion from the drive motor to the agitator and the spin basket. If you can tell that your washer's motor is working but you don't see the basket spinning or the agitator moving, possibly your drive belt is broken.