Remove the gas cap and smell it does the fuel smell fresh or does it have a hint of varnish or stale fuel to it?
You can get a shaker siphon from Pepboys or most auto parts places and siphon the fuel from the tank.
http://www.amazon.com/Hopkins-10801-...=sr_1_1&sr=8-1
If the fuel is stale hopefully there is not much of it.
Add new fuel replace the fuel filter and as mentioned in a previous post purge the lines of any of the old fuel.
Remove all the spark plugs and pull a compression test. while the plugs are out if they look fouled replace them.
If the compression is low across all the cylinders add a small amount of transmission fluid or marvel mystery oil in each cylinder and bump crank it over to distribute the oil along the rings and cylinder walls.
let it soak like this for a hour or so. then crank the engine over with rags covering each hole to catch some of the oil as it gets pumped out.
Then recheck the compression, if the compression has recovered clean up the mess and install the new plugs.
Try and start the engine, if the engine starts and runs great.
If not let us know and we can advise you further.