Backdoor

A: "Why isn't my laptop functioning?" (askong as his laptop cannot be turned on)

B: "Look backdoor!"

A: "You mean backdoors that are installed in some dangerous softwares?"

B: "No, I mean look at the back of the door!"

A: "Oh, I see." (realising that the cable is not yet plugged into a socket after looking at the back of the door)