With the limited information you gave it is very hard to answer your question but to list all the possibilities. First unplug the machine for 5 minute to allow it to reset then plug it back in and give it a try. The more descriptive you can be in your question the more the problem can be narrowed down.
If the dishwasher won't start the thermal fuse might have blown. The thermal fuse helps to prevent damage to the dishwasher by turning off power so that it doesn’t overheat. Once blown, the thermal fuse will have to be replaced for the dishwasher to work. The thermal fuse is usually located in the control panel on the control board or mounted to the bottom of the tank behind the lower panel. The thermal fuse can be checked for continuity.
The door switch, or switches, are sometimes called interlock switches. The door switch prevents the dishwasher from running while the door is open. If the dishwasher won't start, the switch or switches might be defective. To access the door switches, remove the control panel or inside door panel - depending on the model. They can be tested for continuity.
If the dishwasher does not start, the door latch assembly might be defective. These are normally made of plastic and cannot be repaired. If the door won't latch and the door latch is broken, replace it.
Main Control Board
The main control board provides power to nearly every component of the dishwasher. If the dishwasher won't start the main control board might be defective. You should first check for more common parts. Many times control boards are replaced unnecessarily because the problem was not diagnosed properly.
Touchpad and Control Panel
If the touchpad is defective, the control board might not get the signal for the selections made. If the dishwasher won't start and the display doesn't seem to change properly when the buttons are pressed, the touchpad might need to be replaced. On some models the touchpad and control panel are sold together and will need to be replaced at the same time.
If the touchpad is defective, the control board might not get the signal for the selections made. If the dishwasher won't start and the display doesn't seem to change properly when the buttons are pressed, the touchpad might need to be replaced.
The timer allows power to flow to the proper parts at the proper times. If the dishwasher won't start, the timer might be defective. Keep in mind that timers are often misdiagnosed as the cause of a problem. Check other components first before replacing the timer.