Hi, I am Steve, lets get you some help.
There is not a switch on the machine to make the safety guard work it is an interlock device so the guard pushes something out of the way so the machine can operate.
If the machine will start without the guard fitted then the lock that the guard pushes into is blocked so it is not springing back into place and disconnecting the motor.
Because of the type of equipment is is and the fact that it is in Commercial use you really need a qualified technician to look at the device and repair it.