cannot talk in SL

I don't know what's wrong. I see me and all the others on the list conected to voice chat. I can hear what they are talking, but I just can't talk. When I press Talk button the green dotten becomes lighter. Not like the others, where I can see the waves when they talk. Can anyone help me, please.
Must tell that the mic it's working on the other programs form my pc.
Tank You

u have to turn it on in your preference settings. go to the top of your screen and one of them choises .. not sure witch one . could be "view" or "world" anyway. once u click on one of them it opens a pull down window.. look for preferences all the way at the bottom.. u have to go there and set up a button to activate your mic