What settings do you have for Speakers in Tools -> Options -> Audio settings? Is there more than one option available in the dropdown selection box? Can you hear any sound when you press the green test button next to this selection box?
I have the exact same problem. I cant hear neither when i log in on skype or when i am talking to a person. He cant hear me and i cant hear him. But my spotify works and so on, it is not a problem with my headset. Help me!