I have received phone calls on my pc and it was very very clear?

When someone called me from Pakistan on my pc...the call was very clear.


Several weeks later, someone else is trying to call me but i can hear them but they cannot hear me....what is going on?I have received phone calls on my pc and it was very very clear?
There are two possible reaons for this


1) the microphone is disabled from the control panel


2) your connection might had a problem that time.....sometimes it happens with the server that it only receives data but cant send them due web traffic