Hi Ichiro, very sorry we missed your post!

After installing the latest version of Little Musician, did you re-download and import your curriculum content too? If you haven't reimported your content files, please try that and see if it helps restore the missing sound.
If you already have the latest content in your Little Musician and you still don't hear anything, kindly run the Audio Diagnostic Tool and see if that fixes the problem. You may keep clicking on "problem not fixed" in the tool so it will keep trying different solutions. Once you reach the screen with the message "..has done all possible adjustments... contact BrillKids Support" and your sound playback problem remains unresolved, please create a diagnostic report and send it to us at support[at]brillkids[dot]com so we can troubleshoot further.
You may refer to this article for detailed instructions on running the Audio Diagnostic Tool
http://support.brillkids.com/entries/20433747-how-to-use-the-audio-diagnostic-tool