What happens next?

How to reattach a keyboard key
Inspect the back of the key for damage.
Turn the key over to make sure that the part of the key that latches onto the keyboard is still in place. You should see a small plastic piece that will attach back onto the keyboard base.
Compare the key to the base of the keyboard where you plan to reattach it to make sure that this latch is present. If it isn't, then you may need a replacement key.