In the last few weeks, there has been a lot of problems about sound in most modern distro, from Ubuntu, Slackware, and many more. They have confirmed that their soundcard is detected by the kernel and the module has been loaded, but the speaker won't produce any sound. Most of them happened in Lenovo laptops (like my Friend, Anton). The solution i got from several sources are to compile newer ALSA packages, but in Linux Forum, there's a new solution you might try. Look at this thread and give it a try. It might work for you (you might need to change the path, since it's using Slackware)
Update (19 August 2007): Another solution has come up. This time is for users who used Realtek HD Audio. Check this thread for the solutions.