The fan on my MMM broke too.
It is supposed to turn on before the ESC arms. aka when it is on and plugged into Rx but your transmitter isnt on yet. Ill have to send it back to castle, but its cool enough out now that it doesnt need it yet, but by summer it will so I will send it back eventually.
What motor are you using. It shouldnt have shorted unless you screwed through the magnet wire coating. if your worried add a bit of tape or sealent to the end of your screw.