Check to see if the motor is running during the spin cycle. If it is not, you have a bad contact in the timer module. (Explanation: the motor turns in one direction for agitate, and in the other direction for spin. The turning direction determines whether the clutch locks to the inner transmission shaft for agitate, or to the outer shaft for spin. Reversing the motor is accomplished by switching the direction of current through one of its windings - the timer does this. A bad spin-direction contact will keep the motor from turning; but it may make a humming noise because current is still going through the other winding. Prolonged operation in a stalled condition can overheat the motor.)

If the motor is running, the belt is slipping or the clutch has failed.

How old is the washing machine?