Panasonic SC-HT928 Home Theatre Problems

Hi Guys,
I have a Panasonic SC-HT928 Home Theatre system. Just recently, it doesn’t actually have any sound when voices are playing. This happens on both DVD movies and xBox 360 games (eg. the commentary in games). The background sounds, music and sound effects, work, its only for voices.

Is this just a setting or is the system on its way out? I can’t seem to find any settings which fix the problem.

Looking forward to reading your replies.