go into your graphics card and change format from maintain scaling to panel fit this will fix this issue

I had to change the display on my LED monitor to Automatic for the game to display in full screen mode.

You may need to check that if the GC change does not work as mine did not.

On my widescreen displays, I actually prefer the black bars, as they leave the game graphics undistorted. Don't forget, the only resolution for NF is 1024 * 768.

Full instructions, plus pictures, for AMD, Intel and NVidia graphics cards can be found by searching in the Support forum, I replied to one of the threads awhile back and made tutorials for all 3.