This could be a door lock problem OR a main control board issue.
The easiest thing to check first is the control board. Pull the back off of the control panel and look at all of the connections on the board. Look for a burnt out spot. It will usually be very easy to see. The door lock is a series of switches, springs and a wax motor. You would have to test the switches and wax motor for continuity to see if they are bad.