Just looking at the module won't tell you it's "bad" but chances are if you've replaced the plug with a known working one then the module is the next step. You will need to lock the engine to undo the clutch- easiest way to do this without the correct tool is to obtain a length of recoil rope and gradually feed it into the spark plug hole- once there is enough in the bore it will stop the piston going over the stroke and lock it for you to undo the clutch etc.
pleasant
December 2008