How To Repair Dishwashers/Diagnosing a Dishwasher that won't start

Check the power
Check your fuse box for blown fuses or, if you have circuit breakers, check to see if they are tripped. Make sure the dishwasher's plug is secure in the outlet.

Check the door switch
If power is not the problem, try the electrical parts of your dishwasher. The most common part to fail is the door switch, used to start and stop your dishwasher. If the door switch is faulty it may block the dishwasher from starting because it detects the door as always open. Most dishwasher door switches are about an inch long. There are metal prongs on the body of the switch called terminals, which can corrode due to the wet conditions.

Check the timer
If your door switch is OK, check the timer assembly. This controls when and how long power is sent to other components on your dishwasher. If these controls don't receive power, they won't work. The timer assembly contains a motor which should be checked as well. It is often cheaper just to replace the timer motor rather than the complete assembly.

Check the cycle selector switch
These switches indicate cycles for washing, drying, and setting the temperature of the water. If one of your switches is the problem your dishwasher may not start. By testing each one of these parts with an ohmmeter you should be able to determine why your dishwasher is not working. It is possible for other parts to fail but these are the most common parts to check.