Missing volume control

I have a Windows NT 4.0 system where I am experiencing problems with the volume control icon not appearing in the taskbar. This affects all users logging into the laptop except admin right users who can see the icon OK in the system tray.

For administators, checking control panel-multimedia the ‘show volume control icon on taskbar’ is ticked and ungreyed. For users logging on, the above is greyed out and unticked.

I have tried reinstalling the multimedia settings via add/remove programs and have reinstalled the latest service pack. Any ideas please ???