Some users have reported an issue in which music does not show up in the iTunes 10 playlist, i.e. a blank screen appears when the user clicks on “Music” in the left-hand toolbar.
Remove .plist files. Quit iTunes, then move the following files to a different location (the ~ represents your user folder):
Relaunch iTunes and check for proper startup.
Recreate your iTunes library. As described here.
Remove then reinstall iTunes. Failing the above, try completely removing iTunes per these instructions then reinstall iTunes 10.
Reinstall Mac OS X 10.6.4. Download the Mac OS X 10.6.4 combo updater, which weighs in at a hefty 887MB . Quit all open applications and run the installer.