Thinkpads Forum

The key just unclips itself. I've also put the alt key there and it's steady, so I think it's because of the small things that clips into the holder.
Is there anything I can do other than buy a new key?
Here's what it looks like:
http://i.imgur.com/mcIK0em.jpg?1
http://i.imgur.com/BrhT3jC.jpg?1

As long as nothing is broken (I can't tell from the pictures), you can replace it.
Here is a pretty good video:

https://www.youtube.com/watch?v=EU-iMa4WbZw

It helps if you figure out which way the key goes on in advance
and mark it underneath to keep from getting confused.

If it turns out that one or more pieces is broken, you can buy a single keycap and pantograph assembly from various eBay sellers. I found this one with a simple search of "(lenovo,thinkpad) r400 (key,keycap)": http://www.ebay.com/itm/160831662375

I'm really at a loss right now. I've tried to swap the menu key with the fn, and it stays in place (the menu key), but fn still moves. The I tried to swap it with right ctrl and both stay steady in place. What's the reason for this?

There are some tiny tabs on the underside of the key caps, that snap onto the hinge assembly. Maybe, one or more of those tabs is broken off of the keys that don't firmly stay attached to the hinge.

You can change your keymap.
This way you can stop using the broken Fn key and set another key on the keyboard to work as the Fn key.