Mic is not working

Hello,
frends .,.,.,this is Bhavna.,,who wants a help from u al.,.,.i hope u wil surely help me out.,
actually.,.,while chatting on yahoo i cud only hear the sound of the person speaking opposite 2 me.,,.,but my voice is not audible to the other person.,.,.,i dont know why does it happens.,,and i m unable 2 get a solution to this problem of mine.,,.
i m at a learning stage.,,.,and do not know much about computers hardware,.,,
please give me a solution for it as chatting by writing is more time consuming and a wastage of enormous time and energy especially for a student like me.,.,
i dont not know how to activate the speaker of my headphone and
also after recording my voice and saving it.,.,.even then my voice is not audible to me when i play it
thanks frends