daffy I did that and felt such a pr@tt after contacting the help desk. I don't have a sound icon it's a little "wheel" on the front of my lappy which I must have accidentally turned..
Aint got a clue where it comes from, couple people have tried to sort sound out for me. So I'm presuming they check the things you said. Its not on mute. thanx anyway think it needs trashing it is old.
right click on my computer (either on the desktop, or on the start menu) and select properties, then click on the hardware tab and click the device manager button.
Now firstly do you have anything in the list that is got either a red mark or a yellow exclamation mark over it?
if you haven't click the little plus next to "sound and video devices" and post back what is listed under there.