Magic Chef Refrigerator Model # CTB1723AR

Question

The refrigerator appears to be in very good condition. I've owned it for five years, however, I do not know the age of the unit since it came with the house. It has run perfectly as a second refrigerator in our basement. Suddenly it loses all refrigeration....no water leaking even after I left the unit unplugged with doors open for 24 hours. Any idea what may be happening here?
Thank you