Excel won't open files when I double-click them

My Excel, for some reason, decided that when I double-clicked a spreadsheet file, it would launch but wouldn't actually open the file. This has happened to me before, and I found a page somewhere on the net that told me how to fix it. I couldn't find that page, but I did figure out how to fix it, so I'm posting the solution here.

1. Go into Excel Options
2. Select Advanced
3. Scroll down to the General subheading
4. Uncheck the box next to Ignore other applications that use Dynamic Data Exchange (DDE)