DISHWASHER DRAMA

If you can hear the drain motor humming, look for a clog in the air gap. That's the silver dome on the back of the sink. If there's nothing there, you'll have to find the clog inside the bottom of the dishwasher.
Remove the bottom rack. Rotate the short tube that the lower spray arm is connected to about 1/4 turn clockwise and remove the lower spray arm. Remove the screens over the pump assembly. The hole to the drain pump is on the bottom right. If the motor hums, but doesn't pump, and there's no clog, the pump must be replaced.

If the motor doesn't hum in the drain mode, check for power at the pump with a voltmeter. the pump is behind the toe panel on the left. Reaching the terminals to take a reading may be difficult. you can disconnect the terminals from the pump to take the reading only if you use rubberized alligator clips to connect to the wires. If the motor has power but doesn't hum, replace the motor. If there's no power to the motor, replace the electronic control / timer.