Togainu no Chi PC Game Problem

I recently installed the Togainu no Chi game as well as the english patch, and the game seems to be running fine. But there is one problem that I can't get to fix; when certain characters come up, the words they say are in the text, but I cannot hear any voice (like Gunji and Kiriwar). The thing is, at some times in the game, I can hear these character's voices, but at other times, I can't. How can I fix this? Thank you in advance. My operating system is Vista; if there is any additional information needed, I will be glad to provide it. I have been looking forward to playing this game for a while now, and I would really love any help you have to offer.

PS: Sorry if this is posted in the wrong place, or if this has already been asked (I searched but could only find similar problems)