Dern default windows settings
Your issue is as mentioned above, notepad will append .txt to any document created in notepad. When you look at the file it may or may not display the .txt extension. Open your my computer, select view menu, folder options, view tab, under Hidden files click Show all files radio button, deselect Hide file extensions for known file types.
This should allow you to see the "real" extension of your files, then just right click the file and rename, remove the .txt from your .html.txt web files.