I had a 3hp Evinrude a while back. Great little, lightweight motor. I'd probably still be using it today if it hadn't been stolen off my boat in Nassau.
Shortly after I bought it I couldn't get it started, no matter how many times I pulled the cord or cleaned the spark plug. Finally, I took it back to the dealer. He found that there was no spark and traced the problem back to a broken magneto wire. He fixed it under warranty and I never had another problem.
If you've ruled out fuel as the cause of your problem, the next step is to check for spark. Pick-up a new spark plug, as has been suggested. However, before screwing the new one back into the engine, hook it up to the spark plug wire, pull the cord, and see if you get a spark at the tip of the plug. You'll probably have to do this at night or in a darkened area in order to see the spark. No spark, no chance of getting it started. Got spark, check your fuel system again. Fuel OK, time to visit a professional.