New battery doesn't mean good battery. What is the battery voltage? Have you checked valve lash? Did you remove the spark plug and try cranking the engine? If so, does the starter crank the engine revolution after revolution or is the engine mechanically locked up? Have you performed any tests besides trying to start the engine? If so, what tests have you performed?
A lot more information is needed from you for us to help you. I listed several items that could be your problem and none of them may be your problem. From what you posted, it sounds like the starter will crank the engine for a couple of revolutions and then the crankshaft stops rotating - is this correct?
Please answer all of the above questions and I will do my best to help you.
