How should I troubleshoot a refrigerator that is not cooling?
Check to see if the freezer side is working. Often times the cold air comes from the freezer side via vents/holes going from the freezer to the fridge which can be adjusted. If the freezer side is working and the fridge isn't, it's likely these are completely closed or maybe blocked by items in the freezer covering them.

This may not be your exact issue. But, I'm adding it as an answer because I'm sure it will be the source of the problem for many others.