Three main ingredients, Air, Fuel, Spark... It is possible that you are having an Air problem since it has been sitting, and especially if you still have an air box. Make sure it isn't full of mouse nests. This happened on another bike I had. I couldn't figure out why it wouldn't start, I checked it out, and the box was full to the top with dog food, LOL. If that isn't it, make sure your fuel delivery system isn't obstructed. The most common thing is Spark. Pull one of your spark plug wires and stick a spark plug in it, and rest it on a metal part of the motor. Turn your motor over, are you getting a nice blue spark? If so, then you could still be having a fuel problem, if not, then it is either your kill switch ( malfunctioning or off) or your points are dirty, or a wire has been severed.
There is another thing, but you said it was running before you put it away, so I doubt if you developed a compression problem. If you don't have good compression, like 100psi or more, it will either run like crap or not run at all....