can't hear playback sound in protools Le 6.2.2

[greytail]

Just got an MBOX and am able to play I-Tunes through it into an amp and speakers. BUT, after quitting ITunes, cannot playback ANYTHING from Protools 6.2.2. Can't hear imported sound or sound recorded from a mike through the mbox. I see the level jumping up and down..that's it! What could be wrong? I am on a MAC G4, 1.4 GIG DUal. The MBOX is plugged into a dedicated USB on the back of the MAC. Have also noticed that I cannot playback sound from Quicktime movies in a web browser. Added Safari to the list of CoreAudio programs, but made no difference...no playback sound in I. E. either even though Quicktime is listed already as a program that can be used. QuickTime playback is heard when the player is brought up as a stand alone player.