Why won't a 1998 Ford Taurus sho turn over?

Assuming here that the battery has a full charge and the starter is not broke, first try starting it in Neutral. If that works then I would suspect a loose linkage in the gear shift lever. I had a 1995 Taurus that would not go fully into park. After a few days of putting a rock behind the tire to keep it from rolling, I looked up under the steering column and found the 2 screws that secured the linkage to be loose. I just tightened the screws and the problem was fixed. Have someone move the shift lever while observing where it connects up there. Bill V.