My monitor is 1280x1024, but Fallout 4 only gives me the option to run the game in widescreen (16:9 or 16:10). The Resolutions menu in the Options dialog box is blank. Also, Windowed Mode is checked and grayed out so that I can't unselect it.

When I first started the game, it was in a widescreen window across the top. I changed the options to not run in a window, but then it was in a widescreen mode that ran off the right side of the screen. Now I can't unselect Windowed Mode anymore. It looks like it might be centered with the cursor constrained to the screen, but honestly it's hard to tell what's going on at this point.

How do I run the game fullscreen at my screen's resolution? I have an nVidia GTX 980 and am running Windows 10.