hmm... I'd take ur board out, and Try turning it on out of the body (take the board out and plug the battery in)
there are only a few simple causes...
The switch is bad (it got hit hard or something)
the switch is being de-taches from the bord
there is a short circut somewhere...
The thing i'd do would be check all ur solder connections on the board... have u changed ur switch? when did this start?
If everything seems good, what i'd do would be bring ur board to an electronics store, and ask them if they have one of the switches that are on your board, then replace the switch like ur replacing a trigger switch.