Try following this guide: https://help.ubuntu.com/community/SoundTroubleshooting
Did it help?
You can check what sound card you have by typing this in a terminal:
sudo aplay -l
Your output should look something like this:
**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: ALC861VD Analog [ALC861VD Analog]
Subdevice #0: subdevice #0
If you see aplay: device_list:221: no soundcard found..., Ubuntu is not recognizing your sound card for playback. Check that you have the proper modules installed.