Folder Options on Windows XP

The third tab in ‘Folder Options’ is ‘File Types’. In that, I selected File Folder, clicked on ‘Advanced’ and created a new action ‘Open’, for which I entered ‘explorer.exe’ under ‘Application Used to Perform Action’. After this got saved, all my folders are opening in new windows. I have reset the option in the first tab (General->Browse Folders) of Folder Options to “open each folder in same window”, but it does not help. Going back to the third tab, where I created the problem initially, it does not offer the option of deleting or editing this new action that I have created. Can someone help me to get my folders opening in the same window again??