undo programs association

Windows XP SP3 I've inadvertently associated a previously unknown file extension with a program. How do I undo this so that the file extension is again unknown to Windows? Thanks, Dave

May I know the name of the file you changed and to what program extension you have changed it to?

I'm using emacs and I needed to append the file .emacs in my 'home' folder. I created the file and then went to edit it. I did "open with=> emacs 22.3" and forgot to uncheck the "always use this program…" checkbox. Now, the file appears with a file name of " " (blank) and its file type is displayed as "emacs 22.3 file" Windows is taking ".emacs" as a file extension when it really should be the name of the file.

Did you try this? * Right-click on the file * Open with.. * Choose program