It was the question that was worried me for a last week. Actually, my microphone stopped working suddenly on the previous weekends. And my microphone didn't work in Skype nor Gtalk, it was awful!
I was looking for solution for a several hours and found it just a seconds ago! Hopefully it was described here http://preprocess.me/skype-microphone-does-not-work-on-ubuntu-heres-a-fix for Ubuntu (Ideal works under Kubuntu too)
Just main steps (to me in the future):
- Run alsamixer
- Go to Capture devices
- Select capture device (I had two) and highlight it; then pres space to enable - you capture device must be highlighted in Red "Capture" label