Do you have a Yamaha Motif keyboard? This problem can occur after installing the Yamaha software editor application, Motif Tools application or Tyros software. It is not clear if these application(s) must be installed to use the USB capabilities of Yamaha Motif, but it seems likely. Apparently, this software is preventing Pro Tools from launching and uninstalling it doesn't help Pro Tools to finish its launch.
Unfortunately, There is no solution to the problem at this time. Uninstalling the Yamaha software editor application or Motif Tools from the Add or Remove Program Control Panel does not fix this issue. Consequently, there must be elements of the Yamaha software that are left behind and aren't being removed when using the Add or Remove Program Control Panel.
Digidesign Tech Support can only recommend that the Pro Tools user call Yamaha and find out how to completely remove the software editor application. Otherwise, the only other choice is to backup the system hard drive and reinitialize (f-disk) and then reinstall Windows, Pro Tools, etc. Do not install the Yamaha software editor application again. Unfortunately, the Yamaha Motif might not be usable as a USB device and must be connected to a MIDI interface with MIDI cables instead.
Other scenarios similar to this situation are:
Pro Tools will not launch unless the Yamaha Motif keyboard is connected to the computer.