My refrigerator stopped freezing and cooling?

I just bought the refrigerator a week ago from a yard sale and it worked fine up until yesterday night I noticed it just blows out semi-cold air in both the top and bottom. All my frozen foods are thawed now and my ice has melted, and the bottom part the food isnt cold, what could be wrong? It is clean with no dust anywhere in the coils or anything and I dont have money to buy a new one again. =(