I've done everything, but I think the video mode is not affected by the manual controls. The only manual thing that works is the focus. I don't know If the shutter speed setting works fine. One obvious thing that I notice is the ISO. I've pushed down the ISO to ISO 100 and opened the aperture to it's widest point, but still the video looks really grainy
Read more: How to manually set up the controls on the Nikon D3100 for videography?