Starting problems

With ignition key turned to on position for icons and preheat(wait to start)on - after they go out, will not start when go from this position to start position. Have to go back to off position, then turn all the way to start position, in one motion, for it to start. Two weeks ago would do nothing. After it set overnight worked the next day. Purchased this motor home from private seller in NOvember of 2014 and it has does this twice since we have had it.