another thing you can try is to RIGHT CLICK "My Computer" and goto "Manage" then "Device Manager"

Once there you should see all the hardware on your laptop, sometimes drivers get corrupted or you could just have a hardware failure.

Under the Sound tab, see if any of the components have a Yellow Exclamation mark next to them, if so post which component its in and the error that its receiving.

You could also try updating the drivers and see if that solves your problem, goto your manufacturers website (IE: dell, HP, Toshiba, etc) and then to support & download, type in your computers model number (NOT series number) series number will be on the top of the computer and easily seen, like HP Pavililion dv2000 your model number will be more like HP Pavilion dv2556us and can normally be found on a sticker on the bottom of your laptop.

after typing that, find the correct sound driver and download and install it.

if you need any more help, let me know... ill check back here later.

~Raelum