I have a 2005 Taurus with the same problem. The engine cranks ok but won't turn over. My mechanic thinks its the fuel pump and gave me this solution. Turn the ignition key on three times in a row without actually cranking the engine. Turn the key enough that all the idiot lights come on but don't crank it. On the fourth turn, turn the key all the way and crank the engine. This works well for me.