Order a replacement key for your laptop. Key sizes vary by manufacturer if you have lost the key. Order retainers also if they are needed. When the new key arrives , do the following. (That is assuing you need a new key.) Pry a nearby key near the one that fell off of the keyboard.. (Try not to break anything in the process.) Examine how the retainer attaches to the key. Place this key back onto the keyboard.
Pick up the retainer if need it and place it on the area where you will put the replacement key. Place the retainer over the button that detects the key press. The retainer should fit snugly over this button on most laptops. Do not force the button.
Replace the button you pried off to determine how the keys were connected. Snap it back on. Take the replacement key for the laptop you ordered and place it pack on the same way you replaced the key next to it. When it is back on properly, you should hear a firm snap. Turn the computer back on and see if the keys you removed from the keyboard work. If the replaced key does not work after you have replaced it, check the key to make sure the new key was installed properly.
Sometimes it may be necessary to replace the entire keyboard of a laptop. This procedure requires taking apart the case, unhooking the cord that attaches the keyboard and carefully removing the keyboard from the computer. Working on laptops requires skill and patience. People engaging in laptop repair must be careful not to damage nearby components when removing the keyboard. The basic process requires attaching the cable for the keyboard back to the case, laying it down, and placing the case back together.