Diagnosis
This is almost always a power issue, not a machine failure. The most common culprit is a tripped circuit breaker or a loose power cord connection at the dishwasher's junction box.
How to Fix It
First, check your home's circuit breaker panel. Find the breaker for the dishwasher (it’s often paired with the garbage disposal) and make sure it's fully in the ON position. If it was tripped, flip it off completely, then back on. If that’ s good, you need to check the power cord connection behind the kick plate. Unplug the dishwasher or shut off its breaker. Remove the lower kick panel (usually just a few screws). Look for the junction box where the power cord connects to the dishwasher wiring. Ensure those wire nuts are tight and the cord is firmly seated.
If That Didn't Work
There's a door latch switch that must engage for the unit to power on. If the door isn't closing fully or the latch mechanism is obstructed, the unit stays dead. Check for any debris in the latch area and ensure the door is latching with a solid click.
Heads Up
When checking the junction box, if you see any melted wire insulation or a burnt smell, stop. You have a serious electrical fault and need a professional.