I have to turn the water on and off at the wall or it will run no stop, why ?

The water level switch/sensor is stuck. This can happen due to a hole in the plastic tubing or it has become disconnected from the tub, or just worn out. Here is a booklet explaining it: https://dl.dropbox.com/u/8010163/Und...c%20washer.pdf
You may need to get an ohm meter to check it.