Nikon shooting outdoor weather conditions?

I took my Nikon D5100 outside in -2C & it was fine outside, then took it back inside & went to focus in on a plant & the shutter made a weak focusing noise & wouldn't focus. The focus points in the viewfinder were small & blurry. Can anyone tell me what's wrong with my camera? Is it gonna be okay, or should I take it in?

Most likely condensation from taking a cold camera in to a humid warm environment. Think of a glass of iced water. The beads of water on the outside of the glass is condensate. Let your camera warm up for an hour and things should be fine.

Next time, before you come in the house when your camera is cold, place the camera in a plastic bag and seal it. Then, bring the camera indoors and let it warm up for 40 minutes. This will prevent condensation from forming on your camera and lens.

Yup, moisture. Leave it along with the lens off for a few days, it should dry out.