My Nikon D750 isn't working properly anymore and I could use some help if anyone has any ideas. The problem seems to be that it displays the flashing "Err" sign. The main behavior I'm observing is that it doesn't want to properly save photos to the memory card. I can get the camera to auto-focus, and the shutter to press normally, but when I do, it says "Cannot Display Image". Zooming in, it gives me a bunch of boxes with X's, instead of proper file previews. When I look on the computer, there are no files that have been saved at all on the memory card. I tried a few obvious things and none have helped, like a) buying and trying a totally new memory card, b) formatting the memory card in the camera and on the computer, c) trying both SD card slots separately and together. One thing I wondered about is whether the aperture control is broken? However, I can change the aperture normally. I don't see any obvious signs of damage to the camera, but its possible this was caused by the bag the camera was in being dropped for a few feet up. Can anyone suggest what to do?