First make sure that all Microphone sittings are ok in your computer then start the game..
Options > Voice chat > - Enable voice chat : ON
-Microphone input device : select your microphone name
-Activation mode > Push to talk : u have to press the "push-to-talk key" which is normally : " T " to let others hear you, if u didn't press it no one will hear you..
> Voice : u don't have to press anything, everything you say...others will hear
after all of that use Microphone signal level : say something...if it moves everything are good
if it didn't that means that your microphone sittings are wrong out of the game
or u need another one
try now & tell us if everything going well or not...