This is typically caused by an anti flood device which has engaged due to a small leak in the floor of the dishwasher. Try pull the machine out and tilt up gently and watch water dribble out to a waiting towel to mop it up. Turn the machine on again and it should start, however if the leak is still present the fault may occur. Also, many machines will offer an error code when the problem starts to tell you whats going on. Checking your manual will guide you. Leaks mostly will need a techncian and may need the damaged part repleced.