The 5th screen, or center screen, is turned off by default.  To turn it on, check the "Enable Center Screen" option in the dxTop menu.

Steps:

1. Press the menu key while on the desktop
2. Select dxTop (bottom center button)
3. Check the "Enable Center Screen" option

NOTE:  When the Center screen is enable, the screen that was the top screen, is now the center screen.  The center screen is the master screen, so when the home key is pressed you will go to this screen.  The blank new screen is added as the Top screen.