what could be the problem?

My Vivitar 8300s now produces dark bands across each photo, the lighter the scene, the more intense the bands, with or without the flash. It has not been knocked and there is no damage to let any stray light in. On camera, the bands seem quite wide apart but when viewed on a PC, they appear to be very narrow and hundreds more of them. Since new, the flash has allways appeared to be to strong and we have had to mask it. Could there be a worsening weakness in the lenses or in light sensitivity of the camera and, will it be worth repairing it?