1. Open terminal in Applications>Accessories>Terminal
2. Edit the the file at /etc/modprobe.d/alsa-base in a text editor
3. Add the following line to the end of the file and save
gksudo gedit /etc/modprobe.d/alsa-base
4. Now try rebooting your machine to see if the headphones work. If this makes the sound any worse, repeat the above steps, this time removing the line you added the first time.
options snd-hda-intel model=auto
Please note i have not tried this with my own machine but post number #33 in the link below says it should work.
There is also another page in the link shown below about compatability of this laptop with linux that you might want to read.