Dash mileage doesn't show and fuel gauge doesn't work

What is your question?

I have a 2000 Buick regal LS.The fuel gauge doesn't work.It stays on the full mark but every now and then it will go to Empty and the yellow light will be on for a very few minutes.The milage doesn't light up so I can see how far I'm getting before I run out.What could the problem be?How expensive is it to fix?

What makes this problem better or worse?

It's the same all of the time

How long has your 2000 Buick Regal had this problem?

I've only had the car for a few months