Not sure if I can help, but....are you doing the install by following the original instructions, or just clicking and hoping? From a "clean" starting point(no left-over traces of failed PT installs), you would run the installer with the Mbox NOT connected. When the installer tells you to connect the interface, connect the Mbox>wait maybe 8 seconds and then continue. The next most important detail was/is to ignore any popups reporting "New Hardware Found". Don't click on those at all and they will(should) go away on their own
Hopefully you have the authorization code(the code that starts with "DIGI0......"). Without that, you'll be stuck even after a successful install