I had windows 8 pro installed when suddenly internal speaker stopped working. I was using DFX speaker software for a month and for sometime I was experiencing the same problem. But,it would be solved if I closed and reopened the DFX software or change the default speaker. Then, one day it suddenly stopped working. I installed Ubuntu 13.04 hoping for any miracle but,the problem remained same. When in headphone sound comes perfectly but no sound from internal speaker when unplugged. In ubuntu, sometime headphone stops working too. Then, i have to restart again. This happened when i tried to solve from some forums. It creates dummy output profile instead of headphone as default speaker.But, after restart it sets back to headphone.