how are you trying to turn it. By hand there may be enough friction for it not to turn even with th plugs removed. I have to turn my 54 by the flywheel to get enough leverage. The 38 I can turn by the fan belt when properly adjusted. If you are relying on the starter to turn it you may not be getting the best connection electrically to the starter so may want to clean all connections. Don't skimp on the diesel fuel in the cylinders fill them full you are going to change the oil before actually starting the engine any way. May or may not help take a power drill with a flat bit and insrt it in the oil pump tang and circulate oil thru the motor.