How to tell if my dslr camera is dirty or messed up?

I have a nikon d3100. I have not used it much, just every once and a while. I notice when I record video there's a white spot on the video. On the camera screen it looks like a dead pixel but on the actual video it shows up as a white spot. I tried taking the picture of the white paper but it looks ok and photos look ok too even on the screen. What should I do? The camera is still under warranty.

If the camera is still under warranty, this is a good time to have it checked out.

Dirty sensors will show dark spots on your images, which are more noticeable in the sky areas of your images.

You can check for dust by taking a photo of just the clear blue sky and then inspect the image at 100% for dark spots in the image