Uninstall Itunes, and delete all the files except for the ones in the itunes media directory. Then, reinstall Itunes. The reason you have to do this is because the drivers that would support the IPhone have been corrupted.
Yes, uninstall Itunes. There is an article I recommend that was posted by another respondent that deals with this issue, and because of the complexity of the nature of this problem, read and follow the directions given exactly, because you will need to remove the Apple Mobile Device driver, and you could really mess up Itunes if you do this wrong.