I'm having a problem with my Nikon D3100. My photos have a dark horizontal image above the picture when using a higher shutter speed like 1/100 all the way to 1/4000. I already tried to adjust the ISO, aperture, and the shutter speed. I also tried all of the other auto settings but they still have that horizontal line above the photos. The higher the shutter speed, the darker the horizontal line is, although the image below that line is normal. I think it may be the shutter blade's shadow. I also tried to take photos with flash on and flash off, but I got the same result. At 1/100 the horizontal line is not that visible, but it was there when I zoomed in.
Is there any way to fix this on my own?