If your dishwasher isn't starting, one possible reason is a bad capacitor. The capacitor helps start the dishwasher motor by providing a boost of electricity. If the capacitor is bad, it won't be able to provide the extra power needed to start the motor.
There are a few ways to test whether the capacitor is bad. One is to use a multimeter to test for continuity. If the multimeter shows that the capacitor is open, then it's likely bad. Another way to test the capacitor is to use a voltmeter to test for voltage. If the voltmeter shows that the capacitor is not holding a charge, then it's also likely bad.
If you think your dishwasher's capacitor is bad, the best course of action is to replace it. You can find replacement capacitors at most hardware stores. Once you've replaced the capacitor, your dishwasher should start up just fine.