First, make sure you are booting up the laser marker following the right procedures:

1. Connect the power cable to your machine, and then to a 3-prong socket, which must have a working ground wire. 
2. Ground the machine using the ground wire on its back.
3. Connect the protective cover to the machine and close the cover's door.
4. Turn the emergency stop clockwise to release it. 
5. Press the green button and release it. The button should light up when pressed and go out when released. You should also hear the fan inside starting to run.
6. Turn the key switch clockwise, the inside of the scanning head should be active.

If the device still cannot be turned on after following the correct steps, please check whether the protective cover's sensor is properly secured. As shown in the figure.

Alternatively, you can use two wires to short-circuit the interface as shown in the following diagram, and then test the machine by turning it on. Note that this measure allows the machine to operate without the protective cover. Please wear appropriate protective gear during operation to prevent potential injuries.

If the machine still cannot be turned on, please open the case and check the lighting status of the safety relay. Normally, after pressing the reset button, the safety relay should have three lights on.

check the safety relay (as shown).

1. The safety relay doesn't light up 
   Measure the voltage between A1&A2.
   If it is 0, check the wires between the switch power supply and the relay.
   If it is 24V, replace the safety relay.
2. The safety relay only lights up one indicator

   Open the protective cover, stick the door switch with tapes to disable them, and Measure the continuity between S11 & S22, and S21 & S22 on the relay.

   a. If there is no continuity, the issue is caused by the door sensors.

   b. If so, please press the RESET button and measure S33 and S34 simultaneously. The safety relay is defective if S33&S34 is continuous. Otherwise, replace the reset button.