I am of no help to you with my limited knowledge in outboards, but if you post more information others may be able to help! There are some pretty knowledgeable people here.
1) Which motor specifically? 2 stroke/4 stroke?
2) Did this motor ever work while you owned it? If so when/what happened when it stopped?
3) Were you able to try/rule out anything yet?
In general engines need spark, fuel, compression, and timing. So that's the list to check. If it cranks I would make sure it is getting fuel and spark first. This is my general knowledge (probably not even correct!) about motors so you would need to look up how to check those online for an outboard. Others may be able to chime in with specifics.