How did you "insert" it ? Did you open up the "Sound and Audio Devices" at the Control Panel and put a check at the box where it says "Place volume icon in the task bar" ?
in the last days the Sound icon in the tray disappeared. When I try to re-insert it through the control panel I only get the message:
Can't visualize the volume control in the application bar because the application Volume Control hasn't been installed. To install, use the Install Application in the Control Panel.
Well, there's no such application in the Control Panel, how can I proceed?