Easiest thing to do is rule out what can actually stop it firing..
Got gas in the tank?
Fuel tap set to on or reserve (not off..)
Choke on, drain float bowl fuel is getting to the carb?
If so, you know the starter motor is working as its trying to fire, so SEE if it is getting a spark. Remove spark plug, fit HT lead to plug, earth plug to the bike either on cylinder head or exposed bolt on frame and hit the starter (hold it by the lead btw so you don't get a shock) do you see any spark? If no, then check all electrical connections, start with the bikes own before you fanny about with anything to do with the alarm or immobilizer.
Chances are it will be something minor