Volume icon keeps disappearing from system tray

Volume Control - The volume icon does not appear in the notification area (system tray)
Go to Start/Control Panel/Sounds and Audio Devices.
On the Volume Tab under Device Volume, put a check in the box that reads: Place volume icon in the taskbar.(Classic View)

If that has been tried:
Place your XP CD in then go to Start/Run and type in:
EXPAND -R X:\I386\powrprof.dl_ C:\Windows\System32 (X- is your CD location)
Once done: Go to Start/Run and type in: regsvr32 stobject.dll
or
How to fix system tray icons missing in vista and xp
For those who like to do it manually, open the command prompt and type the following two commands one by one:

From the command prompt, type
"taskkill /f /im explorer.exe"
"explorer.exe"

Hope it helps.