I went in to do some rework on a file. Originally, the file was an angel holding her hand out for a little bird to land. There was a photograph background for the sky, a bryce mountain and tree with snow to complete the scene. I opened the file and there were no lights (at all). I put in some lights and suddenly discovered the only thing left was a bald naked lady and the bird. I had saved and reopened the file before so I know everything was there in the file before the last save. Any idea what happened (outside of the usual computer hiccups).