Volume taskbar icon not appearing

In control panel
select 'Sounds and Audio Devices'
select 'Volume' tab
put checkmark (ie click if not set) in box labelled 'Place volume icon in the taskbar'.
click apply, then OK at the bottom.

this appears to be the main fix, or sometimes just a restart will fix a problem, sometimes when my usb ports stop accepting a flash drive, (even though it did a few minutes earlier ) I just restart and/or run checkdisk :)