Do you remember spilling anything on the keyboard ? A mug of whatever, a little movement and a splash onto a small area of said keyboard, it can happen. As to the way the tressle goes together, you'd have to look up some helpful video on YT for example. Clean the underneath with a cloth to see if there's some dried liquid affecting the area. Buttons back on successfully and if it doesn't work, then either 2nd hand, new or aftermarket is the way to go.