Why won't the volume buttons on my Windows XP work anymore?

Out of the blue, the volume buttons on my Eee PC Netbook won’t work anymore. I press the Fn button, and then go up to the volume buttons, and it doesn’t do anything. Also, the volume icon takes itself out of the task bar. Every time I turn on my computer, I have to go in and manually put the volume icon back in the task bar, even though the box is already checked to automatically put it in there. I have no idea how to fix these problems. Can anyone help me out?