Laser is not firing, machine stops

How thick is the board, exactly?
(You might need to measure it with calipers, because half an inch thick is too thick for the machine to focus on without removing the crumb tray and propping the board up on something that is one inch tall, to bring it into the correct range.)

There are some discussions on engraving without the crumb tray here:

Note: On that second one, the laser will determine the height for you if you bring the top surface into the correct range…you can just read it for understanding.