When I hit the mute button on my Lattitude D620, the sound mutes while I hold down the button, but not when I release it. I have to go in and manually change the sound. Also, when I hit the volume up and down buttons, the box pops up telling me how much I am changing the volume, but not accurately. The volume will change, but the box says nothing is happening, then I hit is again and the volume changes by twice what I wanted it to do. How should I go about fixing this? It only recently started happening and sometimes when I restart it works again. Thanks!