The sounds stops immediately if I unplug the laptop charger and nothing will make it produce sound again even with my own sound devices connected to the laptop! I'm using Ubuntu 12.04 LTS on a G570 Lenovo.
Maybe it's a drivers' problem, so be sure of install them. If you didn't install any drivers/your soundcard's drivers yet, you can follow the next steps:
After restarting, it should be working OK if it was a driver-related problem. I hope it works to you and tell us soon!