For remote PC's OS with XP
1) No sound card is available.
Check to see if a sound card is present or if USB sound card is working properly. Make sure the hardware does not have conflict with other devices.
2) Sound card is available, but not the sound mixer.
For older sound cards, the sound mixer to record customer's voice is not present, and sound sharing will not work for this case.
3) Mixer is available, but not working properly.
In this case, the sound card's driver needs to be reinstalled or updated. To check that the mixer is working properly, play a video from the Windows Media player and record it with the Windows recorder. Then, check the recording to be played correctly.
For remote PC's OS with Vista or later
1) Sound device might not be active.
Plug in the speaker or headset to activate the device. In some cases, unused devices go to a standby mode being inactive.
2) Default sound device is different
Go to control panel > Hardware & Sound > Sound > Playback to check of the default playback device is the speaker or headset.
3) Sound quality setting is not compatible
Go to control panel > Hardware & Sound > Sound > Playback > Select the default device > Properties > Advanced > Select the Default format to 16bit 48000Hz or higher. Any other format not listed below is not compatible