Not a lot to go on here.But ,oil engines will not fire without sufficiant cranking speed,they rely on it.Without correct cranking speed the air is not compressed enough to raise the temp in the cylinder to the point where the injected fuel ignites.Tackle the slow speed first.I'd have the starter out for stripdown.Dont discount the head gasket,if its leaking then one or more cyl could be fluid locked,can give same symptoms.is the coolant level ok.
caine
August 2008