Options -> Voice -> voice transmit and voice recive on max, withboost microphone gain, if you still having problems go to windows' controll pannel -> to sound -> recording -> choose you microphone -> and put the microphone boost to the needed level.
Options -> Voice -> voice transmit and voice recive on max, withboost microphone gain, if you still having problems go to windows' controll pannel -> to sound -> recording -> choose you microphone -> and put the microphone boost to the needed level.