Sometimes you find your System Tray Notification Area Icons, like Clock, Volume, Network or Power missing or momentarily disappeared in Windows, here is what you may try:

Fix: System Tray Notification Area Icons missing

Right Click Taskbar and choose ‘Properties’.

Then from the ‘Taskbar Properties’ window select ‘Customize’.

Next, select which Icons and notifications should appear on your taskbar and hit the ‘OK’ button.

If this does not solve your problem, or if you find that the areas are grayed out, try this registry tweak.

On my Vista I found their first instance in Key:

HKEY_USERS \ S-1-5-21-2193082411-1103859620-1337499753-1000 \ Software \ Classes \ Local Settings \ Software \ Microsoft \ Windows \ CurrentVersion \ TrayNotify

You will normally find IconStreams & PastIconsStream in the RHS pane of

HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify

Reboot.
Now enable the system icons using the above regular method. Do note that in case your computer has multiple user accounts you may have to enable icons for each account.

If you are running Windows 7, click Start, type Customize icons and then click Customize icons on the task bar. Next click Turn system icons on or off, and then set Volume, Network, and Power System to On. Click OK, make sure that the behavior for Power, Network, and Volume are set correctly, and then click OK.

Alternatively, you can also use this Fix It solution !