This issue has now been fixed in the latest version of Game Hub. Download the latest version here.
There's currently a known issue where the registry key for the last saved window position for Game Hub is corrupt. This will result in the Game Hub window not being displayed.
Workaround
- Hover your mouse cursor over the Game Hub icon in the system tray.
- Right-click on the preview window and then pick "Move".
- Press a single arrow key once, then move your mouse accordingly to bring up the window into your view and then left click to drop.