Dishwasher won't start. We have a Whirlpool Quiet Wash Plus dishwasher (owner's manual says series

Question

We have a Whirlpool Quiet Wash Plus dishwasher (owner's manual says series 900, 915) and it won't start. We used it last night, and loaded it up today without thinking about it twice, but now it won't start at all - no lights go on, etc. We've checked the circuit breaker, water heater, door latch, etc, and haven't found the problem so far...