Well, there you go you have at least narrowed it down to the problem. I thought that you said you had the Alternator tested. If you did and it was good then you have only a few possible issues. First, did you install/re-install the starter. Is it possible that you did something wrong? Wired wrong or mis-aligned on the flexplate. If it was mis-alinged then it would probably just grind. So if the starter is not even turning then you can narrow it down to the starter not getting power. Check the cables that run directly to the starter. Make sure all of the cables are attached properly.
