Black screen picks up only bright lights

if it is only recording bright light sources then it must be working fine outdoors in broad day light. if so, it means the auto iris of your camera has stucked to minimum opening. was the camera lying idle for long time. try pointing the camera towards low light and bright light with quick moves.some times by doing so it gives a little jerk to the mechanism and it starts working, or lightly patting the camera on the lense side may solve the problem. otherwise let the repaires earn some money.