No Worksheet Appears in Microsoft Excel

Excel

When you open a workbook in Microsoft Excel, you cannot see the file. There appears only a gray screen, even if (sometimes) you can see a formula in the formula bar!

This can happen for several reasons:

Least likely is that your workbook has hidden sheets, such as with a personal.xls file. So, just go to Format Sheet Unhide.
Excel isn't really opening your workbook at all. Go to Tools Options, General tab. Uncheck Ignore Other Applications.
The worksheet has gotten hidden within the application window. Go to Window Arrange, and hit OK.

Note how the closing buttons appear now...

So double-click the title bar of the workbook...

And now notice how the closing buttons appear...