Well, I'm no master troubleshooter so hopefully someone who's more adept will chime in.

In the mean time...

IIRC you need fuel, air and spark for combustion to occur. What's missing for your rig?

Check for spark by removing a plug and trying to start your rig with the plug held close to the engine block. If there's a spark then that should be ok.

Now check for fuel. Does the inside of the chamber smell of gasoline?

As for checking for compression/air, more than likely air is getting in but we can check the compression w/ a gauge although I would expect this isn't the main issue.