Hello Semisane, and welcome to Seven Forums.
Normally you have to type shutdown with a switch like
shutdown /f or
shutdown -f for this. When typing
shutdown by itself, it is the same as typing the
shutdown /? command.
See top
No args item below.

If you would like a shutdown shortcut, you can use the one below if you like.
Shutdown shortcut - Vista Forums
Hope this helps,
Shawn