Unplug it.
Jk.
Anyways, it could just be slow, and you don't have patience. How long do you usually wait? Where does it stop shutting down at?
It could be the type of computer where it gets to a point and you need to hit a button to completely shut it off. I know I had an old Dell that did that. And because you're installing 2000 on it, it seems to be an older computer, so i'd bet you are required to hit that button.