Camera frame missing.

I’ve read everything I can on blender camera, but have not found out how I can get back the solid line framed around the window in camera view. I still have the two dotted lines, but no solid line.
Thanks for any help.

It’s probably because the camera is on a different layer to what you are viewing.

An object other than the camera is being used as the “camera”. Select the real camera and Ctrl-Numpad-Zero.