Microphone problems-help needed!!!?

I was talking to my friend thro Skype and I had yahoo messenger on at the same time. As I felt some disturbance, my friend stopped skype and called me thro yahoo, but I was getting call on skype instead on yahoo and I was able to hear her clearly, but was not audible. I use a headphone with a mic to chat. I tested my mic thro testing some voice in other PC. Please help me wot I have to do now?