Is the door completely latched?
The door may look closed, but may not be latched. Open and Close the door firmly, the door must be completely closed and latched for the washer to operate. Once started, the door will lock, then unlock, then lock again. This is normal, and is a self-test of the lock mechanism.
Be sure that clothing items are not stuck in the door seal, or latch.
Was the "Start" button pushed and held?
This button must be pushed and held until the machine starts, usually within 3 seconds.
Has the "Delay Start" been activated (on some models)?
Some models have a delay start, which, when activated, allows the machine to start at a later time (usually between 2 and 8 hour delay). Verify that this button has not been activated on your machine.