No image in my screen

When you ask for help, give make and model number. In this case, if display is a CRT type (cathode ray tube, not LCD), then a horizontal single line in the center of the screen indicates a lack of vertical deflection. If it is a vertical line in the center of the screen, it is a lack of horizontal deflection. Both problems can be caused by any number of components, all internal, and requires a technican to repair. Lowrance has a fixed fee system for their factory repairs. See their online info for support: http://www.lowrance.com/en/Support/Service-Information/Service-Rates/