Hello.
Have you considered that the laser driver might be damaged?
When you first turn the laser on power is applied to the driver but then on a signal to the driver shuts the control element off or on according to the program.
If the only way to turn the laser off is turning the machine off it´s quite likely the laser driver is shorted. Most probably a MOSFET is used as the control element and you will require to replace it. You may need a service technician to do it.
I hope this helps.
Regards.