I am using Excel 2007.

When I double-click on a file (regardless of whether it is a .xls or .xlsx)
the application starts but the file does not open. I can only open the file
when I select the Office button, choose OPEN and select the file I want to
open.

This is incredibly annoying and something I never encountered before in
previous versions of Excel (just upgraded from 2003).

Any thoughts?

Thanks.