I wonder if the MS Help viewer has opened off-screen or something.
Give this a try:
[ul][li]Hover over the window on the taskbar (the blank window in the popup shown in your screenshot)[/li]
[li]Right-click it, and choose Move (if Move is ghosted, left-click it, then try again)[/li]
[li]Push any cursor/arrow key on your keyboard[/li]
[li]Move the mouse around.[/li][/ul]
If it worked, the window will now be stuck to the mouse pointer and you can position it on-screen.
If that didn't help, the problem may be elsewhere.
Sometimes the MS Help components get corrupted and need repairing. Help file does not display correctly covers some solutions, if that is the case.