Okay, that rules out the motor control. It's going to be either the user interface board or the main control board. I had a similar Whirlpool washer recently where I was able to check the board mounted start switch with a meter. I'm not sure if that's easy to do with this model. In that case, the start button was getting flaky before it went out completely. You should check your connections between the boards, remove and reinstall the plugs. Just to be sure, you are pressing and holding the start button, right?