How old is it? How long has it been idle? Is it gas or diesel? If it is an older gas engine it may have ignition points, they could be corroded and need cleaning. If it is new enough to have electronic ignition there are no points. Also the gas may be old, if it smells like varnish in the fuel tank that is not good, you will need to drain that out and replace it. Chances are that the fuel has drained back and it will take some cranking to get fuel in the carburetor (if it has fuel injection that will not be a problem). A diesel is a whole other matter but that fuel can get bad also.