Trouble starting can be caused by a variety of things beyond the starter: Is the battery strong and are the cables clean and tightly connected? Have you checked the fuel pump? Did you check all the connections after replacing the starter, or check to make sure you didn't accidentally cross any wires? It could also be caused by a short-circuit in the anti-theft system.
For additional assistance, please find an AskPatty Certified Repair Shop at http://www.askpatty.com/search/?type=all&m=30&q=&keyword= and they can help you diagnose and repair the problem.