Invisible Excel Workbooks
You may have had the experience of opening an Excel workbook and then having had seemingly nothing happen. The file isn't corrupt, there's no delay opening a very large workbook, and your PC is operating normally. However when the file opens, the options in nearly all of the ribbon menus will be grayed out, and no worksheet will be displayed.
What's going on? One possibility is that the entire workbook has been hidden. To check to see if this is the case, go to View tab and click Unhide. If a hidden workbook is open, you'll be given the open to display it.