The best bit of luck you have had there is the key itself, I've seen enough of these pop up, in various conditions, roadside, or at tiny's, however 9 times out of 10 the key is missing, which, well, you could always buy an alternative key switch, but really, it's a lot off hassle that comes from a small peice of missing metal.
As blumbly said, your start point is the motor, it could be as simple as gunk jamming the drive cog, causing it not to descend, engaging with the toothed rim of the flywheel, or a matter of the teeth having work or broken on the starter motor, or even a segment of the flywheel (although this is less likely)
or, the gearing system within the starter motor could have failed, the starter motor can be broken up to three active area's, the motor, the reduction gears, and the engagement gears.
The Motor is a high torque electric starter motor, the reduction gears lower the speed of the output drive, and increase the torque, and the engagement gears lower down when starting, engage and turn the flywheel, then retract after starting.
In this diagram, (A) is the Motor (B) is the Reducing Gears and (C) is the engagment gears.
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2013/11/full-5013-13293-vks.jpg)