Recently a gentleman was in the store and had the same problem. He first took the spark plugs out and filled them with Marvel Mystery Oil. He let them soak overnight and then he turned the motor over the next morning to squirt the fluid out of the engine and replaced the spark plugs. This loosens up the carbon build-up and sludge in the engine and allows the motor to turn free. Then once the engine restarts, you should notice a bit of smoke but it will burn off. Adding some Mystery oil to the gas should be of benefit as well, it definitely will not hurt the motor. The lifters are probably gummed up.