Pro Tools 7.x won't launch after updating the OS to 10.4.9/10.4.10, or updating QuickTime to 7.2. The icon just bounces a few times in the Dock.
Updating the Mac OS using Apple's Software Update, and updating specific apps (like QuickTime 7.2 or Safari Public Beta 3) is known to occasionally cause this.
These problems can typically be fixed by running a Combo updater (for the OS issue), or the PreBinding Script from PACE.
Please see the following for additional information: