In some cases, after attempting an uninstall, repairing disk permissions and other common troubleshooting techniques don't help, removing the Digidesign components that did get installed allows you to intsall ProTools.

Start by quitting all applications. Then locate two Digidesign folders located in two different places:

Macintosh HD > Applications > Digidesign

Macintosh HD > Library > Application Support > Digidesign

Drag each of the Digidesign folders listed above to the Trash. Empty the trash and restart your Mac. Then try installing Pro Tools again.