How to Repair a Dead Key on a Mac Keyboard
If you have a non-functioning key on your Mac keyboard, chances are that it is simply loose. These keyboards are designed so that loose keys can be fitted back in place. You don't need to know much about computers or electronics to fix a key on your Mac, and you should be able to do it in a short amount of time. And the best part is that it doesn't require many tools.
Insert the end of your tweezers under the dead key and gently pry up to pop it out of place. Place the key face-down on a table or desk.
Use your tweezers to remove the plastic hinge from the bottom side of the key.
Fit the hinge in the key compartment, making sure that the clips at the side of the hinge connect securely to the metal tabs on the side of the key compartment.
Fit the key back in the key compartment and gently press down until the key snaps in place. The key should now work without any problems.