The first thing I would check is the alsamixer on your system. This is the control panel of the sound on your system.
You need to open a terminal (like xterm), and write the command
You should see multiple sound options. You need to check if there is little MM on top of any of them. If there is, move the cursor to that option and remove the MM, by pressing m on your keyboard.
Hope that helps. If you don't get any sound after that, it might be that your sound card is not detected.