Sudden Weird Change in Desktop Icons

I had an icon for an excel workbook on my desktop that looked like an Excel Workbook item. Now, suddenly, it looks like a notepad icon. When I try to change it back, I'm told there is no previous version of the shortcut (a lie), and the icon file I get when I click the "change icon" button doesn't display anything that looks remotely like a spreadsheet icon.

Can anyone tell me how to either restore the old icon, or substitute an icon that at least looks like a spreadsheet?