I don't what kind of relationship installing pcAnywhere might have with your problem unless a remote user got in and messed with your code. I'm assuming that you're seeing this problem when you're working locally.
If "Show Block Diagram" is not selectable from the Window menu, then the diagram was deleted by doing a Save with Options and selecting the option "Remove Diagrams". If that's the case, the block diagram is gone forever. If the menu selection is there, is it possible that the block diagram screen is just scrolled to a position that you can't see your code? Can you right click on a front panel control and select "Find Terminal"?