Why is my refrigerator warm at the top and in the middle?

Also, food has thawed and the ice is melting on top of the freezer side. The food at the bottom of the freezer is frozen and food at the bottom of the refrigerator is cold. This 1st happened about 2 weeks ago. There was ice built up on the bottom of the freezer. I unplugged the refrigerator overnight and left the doors open to defrost my frost-free fridge. When I turned it on, it started working again, even the ice maker. Now it's warming up again. Any ideas on what the problem could be? Thank you.