how did it fall off, did it pop of and you can't get it on or did it break. I'm telling you that you can put it back on yourself, its just a little hard to figure out how. It took me a good half hour to figure out how they go on, but you can fix it yourself i promise.
Heres what you do (i'll try but this would be easier with a pic or diagram), when the key pops up there are two pieces of white plastic that fit together. usually when the key pops off, they become disconnected and that is why you can't put the key on. If the two whit pieces fit flat you can put the key back on just by pushing ti on. If not you have to fix them so they are flat.
To do that you have to take them off the comptuer completely.
you will have to white pieces of plastic. on is the outside piece that is shaped like a U and the second is the inside piece that looks like a square. and it has two little pegs that fit into two holes in the middle of the larger piece. you alight those, you will have to twist it to do that. they should be crossed together at that point.
Then you have to put it back on the the computer. You do this by starting from where the bottom of the key would be. You take the interior or smaller piece adn slide it into a small little bar so it sits below it and then lay it down toward the top. the larger pieces will snap into two small holes. then it should lay flat. Then you can just snap the key back on.