You can download this tool and play with it. It will help:
type this in the terminal:
sudo apt-get install alsa-tools-gui
but you likely have a hardware problem.
After installing this tool you have to see with of the applications in this collection, will work for you, and when you open an application you have to play around with it to see if it will fix the problem or not, all of them have a restore option so don't be afraid.
this is a list of apps that will be installed, to open one of them copy paste it to terminal:
echomixer, envy24control, hdajackretask, hdspconf, hdspmixer, rmedigicontrol
with this app you can remap your speakers so to work correctly...