Solved—I hope. So I had the same issues with my Whirlpool WDF510PAYSA model dishwasher. After trying to recycle the power and fiddling with the latch switch, it still would only fill and drain, but not wash. I finally pulled it out (while still hooked up) and checked the pump connections. I had noticed that after filling, it sounded the circulation pump was trying to work—slight pulsing hum. I then hit the Start button, and once the fill cycle ended, I grabbed the pump by hand and twisted and shook it in its “flexible” mount. Either a connection was loose or debris was lodged inside—either way it sprung to life and began pumping water through the spray bars. Problem apparently solved! I don’t recommend working on the machine with the power on, obviously…