I agree with tezza - the first step is to check whether there is spark - though I wouldn't do it his way because it hurts too much if the system works. Remove spark plug from engine, connect plug lead, hold or clamp metal base of plug against cylinder head, and pull the starter. Watch for spark across the plug gap. If there is spark, tell us and we can go into the next steps (which are checking for compression, and for fuel actually getting into the cylinder).
