I accidentally detached a button from my compaq presario cq40 laptop but it's not really broken and i can't attach it. how do i attach it again?

Sometimes if you are lucky you can just put the key level where it goes and press firmly but not excessively and it may reseat itself. If this does not work, you should make sure that the plastic piece and the key are lined up appropriately and then secure them to the base. Make sure the rubber stopper is in the center of the key seat so it can press the key when the button is depressed.

Good Luck,

NOLA Tech