Ok lets see:
I'll go with this scenario
1)Your compression is good
2)You have fuel
3)May or may have pulled valve cover
and inspected valve train, if compression
is solid then you may not have
4) You have spark
Have you tried using carb cleaner to start it,
or even starter fluid(although I never recomend that)
that would also rule out water or bad fuel.
If yes and it still doesn't start then I would say the engine
is not breathing.
I have had this happen before when a converter or muffler has
collapsed inside clogging the exaust and not letting the engine
Try dropping the front pipe at the manifold or at the cat, as long
as the pipe is open and then try it.