My Kenmore Frig is not working its only 4 years old and I cant figure out whats wrong with it?

The freezer still works but not as good as it used to. The frig itself does not work at all. I tried everything defrosting and cleaning it, I am not sure what else I can do? Any suggestions about what it can be. Sears won't fix it and they charge way too much. What can I do?