Help!!Has anyone encountered this problem? My ATC window has changed to an opaque blue with white lettering partially blocking the instrunment panel or the view. How can I restore the default window?

Sounds like you undocked it somehow. Try right-clicking and selecting Undock from the popup menu.

Thanks for the help but the problem seems to have been solved. After 2 days the default ATC screen reappeared as mysteriously as it had disappeared without any action by me. Another instance of the weird ways of computers?