Why is the microphone not working in Skype?

Question

Skype

There is a laptop Lenovo Y50-70. The laptop has two connectors: S / PDIF and a combo headset jack. The headset is connected via an adapter to the headset jack. Skype can't hear me at all. I tried to test through the "Sound Recording" - it's heard perfectly. The interesting thing is that sometimes everything in Skype works fine, but after a while, right during the conversation, I become inaudible.
I already don't know what to think. What could be the problem?