You must have full Administrator privileges to set the default program to launch when files with no extension are clicked. From a DOS prompt:
assoc command with the extension
. (which is used to denote the case where no file extension is present) and specify "No Extension" as the file type to associate with such extension:
assoc .="No Extension"
Now use the ftype command to specify the command to run when a file with no extension is clicked (the following assumes the latest version of Vim is installed in its default location on the
ftype "No Extension"="C:\Program Files (x86)\Vim\vim74\gvim.exe" "%1"