Try deleting the Digidesgin Databases by following these steps:

1. Quit ProTools and all applicaitons.
2. Inside each mounted hard drive, open Digidesign Database folder and trash all of it's contents (volume.ddb and/or cache.wfm).
3. Inside the Mac HD, open Library > Application Support > Digidesign > Databases > Volumes. Trash the contents of this volumes folder (there may be several files with odd names inside).
4. Empty the trash and try ProTools again.