SOLVED! My Viber Runs, But the Window Cannot Shows

At times, Windows applications such as your Viber messaging, or Adobe Reader starts, but the window started in a position which is out of range of the visible screen. To move the app window back to the visible screen range, do this:

1. Start the application, you should see the app on the task bar. It runs, but the Window is not visible
2. Hold SHIFT key, right click on the task bar icon of the app
3. Select Move, now press the arrow keys of your keyboard. Depending on to which side the Window has gone beyond screen range. For example, if the application window goes to the left side, press RIGHT ARROW key, until the window frame of the app reappears again

Now you should be able to use your mouse to control your application window again.