crankshaft timing issue

[bryan@cedainc.net]

Attempted to break loose the 22mm nut on crankshaft (wanted to replace seal & timing case gaskets) & no luck. I marked the crankshaft position so it lined up with the crankshaft sensor. Sensor was very gummed up on the end; I don't know how it was operating. I lined up these marks but now when I try to start the care, I get a backfire and no ignition. Could I have screwed up the timing that much? How do I solve this problem? Thanks