It sounds as if the ribbon cable has come adrift. If you are unsure at all then wait till you get hold of someone. It should just be a matter of switching off at the wall removing the case and pushing the cable firmly into the sockets and then switching on.
As I said if you are unsure about this at all wait till you get hold of the friend who fixed the PC. Its very simple but I wouldn't want you to accidently damage or loosen anything else.