In these cases, it is strongly recommended that you clean your system by uninstalling all Autodesk products and supporting applications (add-ins, utilities, enablers, etc.), and by removing related files and settings before attempting to reinstall. The end result is a clean system on which you can install your new Autodesk product.
Autodesk - Autodesk Revit Architecture Services & Support - How to remove all Autodesk products from a Windows system
This is pretty drastic stuff, but sometimes it is the only way...