Hi,
Did it ever have a coin switch? If it did I would check the wiring to the coin switch to see if the wires are touching. If the switch is still present, then the switch might be bad.
If that's not the case, the next thing to check is the camera relay. This is the box that sits on top of the camera and plugs into a socket on top of the camera. This box contains two sets of relay switches. When you turn the keyswitch, one of these switches will engage, starting the camera motor that starts the whole sequencing process. The contacts on this switch (inside the camera relay)will sometimes get stuck together because of electric arcing. Since the switch never disengages, the photobooth runs continuously. You can open the camera relay by removing one screw and opening the box. You then may be able to see the switch that is burnt. If so, use a nail file to clean the contacts or replace the relay. Sorry this was a bit long. Hope this helps!