By any chance, are you trying to install the latest Revit while uninstalling a previous Revit? If that's the case, then that would be the cause for your issue. Other Autodesk installations can kind of conflict with each other when they're running together.
If that isn't the case, then I highly recommend restarting your computer and then immediately trying again once it restarts. Because, in this case, a set-up process is open somewhere (possibly in the background) and restarting is the quickest way to shut it down.
