There is a known issue with Ventrilo and some microphones that will cause your voice to "fade out" sometimes to nothing while talking. We have found tweaking the microphone with these settings should help you resolve the problem. These tweaks will need to be done inside the settings for your microphone itself.

These settings can be found in different places depending on your hardware setup. Generally you can find these settings inside of the Windows Control Panel under "Hardware and Sound". If you have custom drivers setup for your microphone you will need to check the application that manages your microphone.