JSI Tip 1629. Does your Taskbar disappear when you move the mouse cursor near it?

It is not just being playfull. 

The subject behavior is normally the result of a corrupt registry key.

To fix the problem, use Regedt32 to navigate to:

KEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Explorer/StuckRects

Delete the StuckRects key.

Close every open application and System Tray icon that you can.

Shutdown and restart Windows NT.