Camera Sometimes Argues With Me.

Salient facts:* newbie, so I have a feeling someone's going to think "WTF, you don't know that? That's obvious!" or similar. It probably is, but I don't. (Hating asking for help doesn't help.)camera is a Nikon D7000.currently trying to use Manual mode more. I kind of...never do, which is why now I'm wondering a thousabd things.current lens: Nikkor AF 28-70mm.Question: Why does my camera sometimes refuse to take a picture, for lack of a better way to put it? Literally: I'll press the shutter and hear the motor whir, etc...but it simply won't click. My assumption, and I think it's a fair one, is that this is because of clashing settings I'm unaware of or perhaps the lighting where I'm trying to take the picture (which still kinda has to do with settings possibly clashing that I need to change), not mechanical error at all.What kinds of issues might cause this? Does what I described make sense? Feel free to ask for clarification; I'm uncertain what other information is necessary. via /r/photography http://ift.tt/2fXW5EG