If you start QViewer and no window appears, it may be that your QViewer window is positioned off screen.  In this case you will see the QViewer icon in the windows taskbar but no Qviewer window to work with. 

You can correct this issue by using the Windows Move window command. 

1. Double-click the QViewer icon in the windows taskbar. to ensure that QViewer is the active application. 

2. Press Alt-spacebar on your keyboard. The Windows "window" menu will appear. 

3. Using the arrow key + enter, or left-mouse click, select "Move" from the window menu. 

4. Use the arrow keys to move the QViewer window left or right until it appears on the screen.  Press enter to finish the move.