The keys on the majority of Dell laptops are held in place with what is called a "scissor" component. The two scissor components work alongside each other, along with a small spring, to provide the "bounce" needed to raise the laptop key up to it's original position after you press it. If one of these falls off, it's possible to put a key back on a Lenovo Laptop Keyboard with out too much trouble.
Determine if the scissor keyboard component is still all in place. If not, you will have to replace the missing scissor component. Position the missing piece of the scissor component over the keyboard, ensuring that it aligns with the four points. Press the scissor portion into place until you hear a click.
Use the brush to clean any debris off the Asus Laptop Keyboard beneath the scissor components.
Turn the key over. Use the brush to clean out any debris on the underside. Examine the scissor connections on the bottom. If these are broken, the key will have to be replaced.
Position the key over the scissor components. Ensure that the key is aligned in the proper position.
Press firmly down on the key until you hear it click.