I had this really annoying issue with Win8, and so did a few others in Netlandia. I'm pretty sure this is the solution. Opening the start button and right-clicking 'This Computer' --> 'Manage' refused to open the management menu/snapin. Instead, notepad opened an XML file for editing. The Advanced button in the firewall settings did the same thing. Others who had this issue did not even get the notepad to open. I use notepad to edit XML files (.xml) and set notepad to be the default opener. Unexpectedly .msc files also then opened with notepad. .msc can contain various scripts, including XML. --THE FIX-- Go to file associations and open the list of default apps for each extension. The .msc extension should be set to open with the default mmc. No need to butcher registry like I did.