First things first: good plugs? They spark in a different machine?
Good connections thru-out?
Then, you almost certainly need a wiring diagram to know where to start tracing: battery voltage at battery, then at key switch, then at wherever it goes next.
Kill switch NOT grounding ignition?
It seems to me, if it was running when parked, it seems very unlikely that a major component (other than battery) has failed just from sitting. Much more likely that it's something related to sitting - corroded connectors, etc.
Good luck with it.
Kirk