The car has 88K miles on it. Was running fine until yesterday. I changed the water pump and timing belt. I aligned the timing marks, turned the engine two complete revolutions to make sure the marks were correct. I then removed the belt, replaced the two bearings, replaced the belt, and reinstalled the tensioner. After putting the wheel back on the crankshaft, I was going to rotate the engine two revolutions to check the timing marks. However, the flywheel cranked about three quarters of a turn and then stopped dead. I can't budge it. Any idea what I have done wrong?