you're SURE the volume bar was there.
Are you talking about Windows system speaker volume OR 3rd party sound controls (Sound Max or other)??
In my case the box to check to "show volume control on taskbar" is located in Control Panel>sounds & audio devices>Volume Tab. Check to see if check mark is still in box. Add if not & Apply & OK.
You could also check (slim hope) CP>Task bar & start up menu> customize which would apply if no volume anything is still on task bar (nothing to click on to bring up volume control). Good Luck!
My window xp volume bar (green color bar appear on the bottom right for few sec when adjust volume) went missing for no reason. Do anyone know how to make it appear again? thanks.