If you know your way around a Nikon camera body, then you might not find this post useful. However, If you are new to Nikon, and you find that the focus points you see through the viewfinder are frozen or stuck, DON'T PANIC! Your camera is most likely just fine.
Frozen focus points happen a lot more often than you might think and I know the first time it happened to me, I was in a complete and total state of panic.
You have most likely just accidentally activated “Focus Point Lock.” No problem. Here's how you fix the frozen focus point problem.
Change the rocker switch on the back of the camera from L to the white dot. The video above illustrates the perfect way to achieve this. That's it! It really is that simple.
If that doesn't fix your frozen focus points, then try a hard reboot. Turn off your camera. Remove the battery. Brew a cup of coffee or tea. Replace the battery. Turn on your camera and try again. If the focus points are still frozen or stuck, then your Nikon camera might be in need of service!