v81 series 2

I have a client who's dgn file has stop displaying the drawing elements this morning. They state the drawing was fine the first time it was open and later when opening it, the drawing no longer displayed anything. I am getting the same results when I open the file. When viewing the levels display the drawings levels still show as being active and used in the drawing. I have looked at the level manager and the display column for the levels used are checked. I have tried edit>select all and nothing highlights in the drawing. Any ideas as what is wrong and how to correct is greatly appreciated.