excel file won't open

been working on an excel file that started taking longer to do things like delete columns. I saved the file and kept working. now I can't open the file. I've updated ms excel, shut my mac mini down and restarted. It still won't open that I can see it, but when I tried to open a copy, I get a message saying 2 copies of the same file cannot be open at the same time. so maybe it's open, only somewhere that I can't see it? help!