Shooting black and white on a nikon d3100?

I know how to shoot b and w ( menu - picture control etc ) but when I click on picture control it says "this is not available with current settings " how do I change this so I can shoot b and w?

I can't answer your question specifically, as I don't know the camera you are using. However, I would say this. I feel it is always better to shoot in colour, then use a photo editing program to make a b&w copy.

You far better off shooting in color than changing the photo to Black and White in post production because you would totally be kicking yourself for wanting a shot to be taken in color, but the settings is still in Black and White.

It's probably available if you actually use the camera like a DSLR (M, A, S or P modes), but you're far better off shooting in colour and editing to B/W in your computer.

You are really wasting your effort by trying to shoot BW in camera. You really want to shoot colour then process into BW to make the most of an image.