I would try to isolate if it is fuel or spark. To check if you have a fuel issue try pulling the air cleaner out and try a getting a can of starting fluid or taking the air hose of at the trottle body and poor/splash a couple of table spoons of gas into the throttle body. put it back together can crank it over if it runs for a moment then the problem is fuel if it does not them it most likely a spark problem. you can also pull a plug wire put a screw driver in that will stay in it with out damaging the wire have someone crank the engine over while keeping a metal part of the screw driver about 1/4 from some metal looking for a spark jump. This will allow you to focus on the half that is causing you problems. I don't know could your drive belt have broken?