Black Rectangle on my screen

I have just installed TightVNC server on my hosted Ubuntu using this tutorial

I can't see my xfce4 menu usually on the top left of the screen where there is red arrow as attached below. The black rectangle is draggable on the screen. Can someone help out?

The issue was that I did not select the default configuration when I first logged in to the box.

To solve the issue , I used this command rm -r ~/.config/xfce4 and rebooted the box. When I logged in, I selected Use default configurations. For more reference, use this guide here