More detail please. Do you not get any sounds at all from anything? ... check/update your sound drivers. Check your speakers are plugged in the right jack, have power connected, and they are turned on.
Just browsers? ... make sure you have needed add-ins like flash player, etc that the site is requesting. Also make sure it is not muted. Check the settings in Control Panel > Sound and run through Configure ... Test to make sure you hear sound there.