If the washer won't agitate at all, but the motor and belts are turning,
then you may have drive coupling or transmission issues. In this case, it
is well worthwhile to have a technician check the machine to verify this.
Sometimes, the base of your agitator can strip out, especially from
overloading. In such a case, the splines are damaged inside the agitator,
and can be seen after the agitator is removed.

Mike