The Intel Corporation NM10/ICH7 Family High Definition Audio Controller is fully supported out-of-the-box, so that's not the issue.
Did you install any proprietary drivers (for example, from Applications > System > Hardware > Proprietary Driver Manager)?
What is your laptop model? Check the sticker on the bottom if you need to to find this out.
When you click on the volume button on the top-right panel and go to Sound Settings, what happens when you try every possible option in the settings under the Output tab?
If still no sound, do this:
Hit F12 on your keyboard and run the following one line at a time:
This kills all sound and starts it again. Do you have sound then?
If not, again try every possible option in the settings under the Output tab.
What's the result then?
If none of that works, I'm rather stumped, but if you want, you can install this
(it's free), and I'd be happy to see if I can myself discover the issue on your machine at a time good for both of us.