Hello Bonnie,
All these answers but no one got it correctly. The problem is usually a defrost timer switch that usually turns on for about 15 minutes in a 24 hour period to defrost the freezer coils from any built up ice that may have formed when in the off /cold mode. If this switch dies then the freezer will warm up either due to excess ice, or just the heat from the defroster depending on the mode it was in when it died. This switch is located usually on the top side of the refrigerator plastic paneling. The cost is minimal for the part which is about $30. The actual location of this timer depends on the make & model number of your unit. Another thing to check is the vent holes (make sure they are clear of obstructions) that go between the fridge and freezer which can be checked with the back panel of the freezer removed.
Good luck!
Rich Lilja