Not a mechanic, but had the same issue on a friends boat and it was the power pack. Take one cylinders spark plug out, start the motor and check for the spark. Do this until you find out if all 4 cylinders are sparking, if the are not sparking you found your problem, and can trace it back. Do a little investigating on your motor before you start swapping parts, that can get expensive. If I had to bet it is the power pack.
Find the model number of your motor, and go to this website it gives you pretty good schematics, while trying to trace a problem.
http://shop2.evinrude.com/ext/index.aspx?s1=1e80cd189ca740acefb14db429fa55f2
Hope this helps