This happend to me on the weekend. Very bad nose dive landing.... The ESC wouldnt arm...
I cut the switch off and just wired the switch wires together, and VOILA its working again... I heard these have got problems with the switches?
Its about the only complaint people have of the MMM- dodgy fans and switches. never had any issues with my fan or switch & they are both about 3 years old now ( MMM V1 )' other guys have less luck. Its no biggy to solder on a better switch though.