I'm going to go out on a limb here and suggest the starter isn't engaging the ring gear. Here's an image, which I'll describe the parts so hopefully you'll get it.
The blue arrow is pointing at the starter motor. The green arrow is pointing at the starter gear. This engages against the large, rusty gear (ring gear on flywheel) which the red arrow is pointing at.
In order for the engine to start, the starter gear is pushed upwards towards the ring gear. While the starter motor is spinning, the starter gear will engage the ring gear and cause the engine to turn, thus allowing it to start. What I suspect is happening, and what was happening to this guy is, the starter gear is not making its way up the starter shaft. It's stuck where it's at (down low). You need to get this to articulate up and down the shaft. There should be very little pressure holding it down. There's only the very thin spring (I believe it is silver-ish in color in the video) which pushes the gear down from the small hat on the top of the starter shaft (pretty much where he's pointing the nozzle of the WD40 can at).
To get it to move, use a small, flat bladed screwdriver. Place it between the starter gear and the metal piece just below it (near where the green arrow is located). Gently pry up on the gear to see if you can work it loose. Like I said, it should come up fairly easily. Most likely something is just barely keeping it in place. Once you've overcome that hurdle, it'll pop up just a little bit, then should slide up and down fairly easily. You might need to try in a couple of place around the starter gear, or possibly in the same place while turning the starter gear by hand.
Also, have no fear about the WD40. It can only help and will not hurt anything in this area of the engine. Not that WD40 hurts things anyway, lol.
