1) Make sure that you or the other party has not muted his microphone.
2) Make sure you or the other party is not running other video conferencing software on your PC, eg. Skype. If you are, please make sure you quit those programs, and then restart VSee. (You can restart by going to your system task tray at the bottom right of your desktop, find the VSee icon. Right click on it and select "Quit." then go to your program files and start VSee again.)
3) Upon restarting VSee, please go to your VSee contact list, under Settings, go to the "Audio and Camera setup" and make sure you have selected the right audio input and output. Use the test sound buttons to verify if the input and output are selected correctly.