Is it sound like something inside is moving?? Krr krr krr sound when u shake it....
There must be cover on the headphones. Muffler type thing on both sides. Its removable , remove that. Now u see screws on the inside. Remove them. Now open. The magnet may be out of place. Put it in place and see if it works now.. If not, check cable for breakage. Replace cable if possible. Then it definately will work. If not, buy new.