there is a sound in game but when i talk with the characters i can't hear their voice
i watched the gameplay video in youtube ,there was a character's voice
but in my game not
what am i doing

my english not good sorry for that

Are you running the game with a 5.1 speaker system?
Could you provide some information on your computer/> Dxdiag will probably do it. To produce it, press Start - Run, then type in "dxdiag". "Save information" to the text file when finished.
It is the problem that arises from time to time, and each time I forget how to solve it. Maybe just because I have never encountered it on any of the computers I had or happened to work on. The solution is something along the lines of reinstalling your Realtek drivers (if it's the case) or OpenAL that seems not to work good sometimes - or, perhaps, it is that the version on game DVD is not the correct one.

Or, perhaps, the problem is the volume and/or configuratrion of side speakers?
Someone had the problem that he can't hear the voice when it stood in front of the character, but he can hear the voice when he stood by side of the character.

You could also try reducing your sound hardware acceleration:

In Windows, go to your Control Panel > Sounds And Audio Devices > Audio > Sound Playback (Advanced button) > Performance. Then reduce the 'Hardware Acceleration' slider by one or more notches.

Some of the OpenAL packages aren't compatible with the game, you'll get missing character voices. Try installing the latest version http://connect.creativelabs.com/openal/ ... Items.aspx