Missing volume icon

go and open regedit from search, by typing in "regedit" into the search box

on the left side of the regedit window, expand hkey_current_user, then software, then classes, then local settings, then software, then Microsoft, then windows, then current version, then tray notification,
then on the right side of the window select Icon streams and past icon streams and delete them if they are still there, a warning message will come, click ok

then open the task manager by pressing alt control delete,

then go to the processor tab and go to the explore.exe and right click it and press restart, then again go to the explore.exe and restart it again, this should restore the volume icon on the notification tray.