Why is my Appature F - Stop stuck at 0?

I have a Nikon D7000 only got it a few weeks ago and am still adjusting to it. As far as I know I've done nothing out of the ordinary with it but when i turned it on the other day I found my F stop was stuck at 0 and i'm unable to change it, I have tried in all modes (i usually use manual) but it won't budge, there's like a little triangle that looks like a steep hill sign before the F which is not usually there. The shutter speed and everything else can still be adjusted fine. I have looked through my manual but can't find anything helpful.

Maybe you need check if your lens is connected properly or if the contacts are clean.

You are not getting a connection. Two likely causes are the lens is not stuck on all the way, or it is not the right lens. If you got an old Nikon, there are many diffrent ones through time that will mount but not connect. Or you got the wrong one all together. If you have a Sigma or Tameraon etc, those are made in many diffrent mounts. You may have bought the wrong one.

To me it seems to be a connection problem. Having a proper mount always do not ensure the connection. I had a similar problem with my Canon and could not change the F stop from zero. I sent it back to the company and they told me it had some connection problem which they fixed while returning the camera back to me. It is working perfectly now.