you may be able to right click on the task bar and in properties restore defaults.
Or the volume icon could be selected from there.
On xp ,so hope it works.
Inside the Control Panel list, click on "Sounds and Multimedia". A window pops up with options...below the slider-bar for "Sound Volume," there's a little check-box that says "Show volume control on the task bar."
Click in the little white box to the left of the words, so that a black check-mark appears...click "Apply" at the bottom of the window, then click "OK".