Off the top of mhy head, and I may be wrong but, you may need to go into control panel, find the speaker control, and retick the box to say keep it visible.
Right click on blank space in centre of Task Bar on which your Speaker Icon was originally. Then left click 'Properties' in the opened menu and on the page headed 'Taskbar and Start Menu Properties', click open 'Notification Area' and make sure that there is a Tick in the box shown as 'Volume'.