Freezer not working. I have a bottom freezer. It is 15 months old. I used to be able to hear the

Question

I have a bottom freezer. It is 15 months old. I used to be able to hear the fan motor kicking in all the time. Then for a while it was really loud and then it went back to normal. Now I can't hear it at all and nothing is freezing - not even water. I turned it off and defrosted it. When I turned it back on....nothing. The fridge is fine. The alarm was on when I came home yesterday. The display said food has to be consumed immediately and to check freezer temp. What's wrong?