Ventrilo's voice activation can be really annoying with the settings. If you have too long of a delay, then you can stop talking and won't be able to talk again for x seconds. My problem always was I would talk at different volumes and sometimes it wouldn't pick up.

One way to check the way its working is to just watch on your screen as you talk to see if your Mic is queing up. Your sound settings won't change in any way, assuming you're using the same headset.