If you can see the extentions, change the .xml to a .txt
Try running Notepad as administrator and dragging the .xml file into it.
Another resolution maybe the file is corrupted or read-only, try editing the properties.
Worst case scenario, re-download the profile. Don't change the extensions, just right-click > open with > Notepad.
Make a back-up copy of any files before you edit them and move them from a SVN folder, if it is in one.