Can't Hear Music

[Deb Hagen]

Tried to listen to a music CD for the first time on my PowerMac G4 in 
iTunes 4.  The song title appears, slider bar shows the song is 
playing, but I can't hear any sound!  Checked System Prefs - nothing is 
muted, "built-in audio controller" is selected, Apple Pro speakers 
plugged into minijack port...System event sound files are audible and 
announcer can be heard.  Can anyone offer a clue?

TIA,
Deb Hagen