I had an issue like this once, but the only way i was able to fix it was by buying a USB headset and going from there. The good thing is that the connecter from the USB actually converts the USB slot into a set of audio ports, one speaker one mic.

Might I suggest.
This

Check with the sound recorder. Are you able to hear sound if so then try using Yahoo Messenger for Voice chat and see whether you can hear them speak or not.

i'm going through the same problem on a friends computer...i've tried using a dif. sound card but to run into the same problem...occasionally i'll get some windows sounds but no music or nething from any program.

First are you using the correct drivers. go to the system properties and look if the sound device has a red X or yellow question mark or yellow dot with black exclamation mark ! if any of these condition exist, fix then got to the next step below

go into control panel go to sound and audio then sound tab and ensure that the correct sound devices is selected as the playback device. then go to the voice tab and test the hardware.

i m not be able to do voice chat at yahoo mesenger .Can anyone tell me what i do? or what software i instal to do voice chat at yahoo mesenger?