I am bothered because you say it doesn't even spit or backfire.
1. You will know if you have fuel or not, easy to view.
2. You can check compression by compression check or even turning engine over with finger over spark plug hole.
3. You can check spark by turning engine over with SP wire to ground.
4. (as johnracer and bigray said) valves may open all the time.
I vote for #4
Dave