It Disappeared!

I've been using Excel since it's inception, & I've never had this happen to me before. I hope it's a silly but quick fix, b/c I need to finish my work...

I was working on a multi-page spreadsheet, when I needed to open another one. I tried to tile view them, and sheet B came open, but I don't know what happend to sheet A. Long story short, I shut all my work down, then re-opened Excel. Well, All I get is the blank blue screen, it says the spreadsheet is there, but it's not. I can go in through a file search and find it, or try to open it from the Excel menu (on Windows 7), and I can see all my work is seemingly OK, but any way I try to open my sheet it will NOT open. I have even tried to copy out of the preview in file view, but it won't let me paste it.

Does anyone have any suggestions as to what I can try? This is a mechanism by which I have been tracking work for months and it is crucial I get it back.

Thanks a million!