Hi,
Does the compressor run continually trying to drive down the temperature?
Is the evaporator unit in the freezer compartment icy cold to the touch, (be careful when you go to test if it is or not)?
If the compressor is running and the evaporator unit is not cold then there is a problem in the sealed system.
This could be due to a blockage, a faulty compressor or a lack of refrigerant.
Is there an oily residue below the compressor or condenser coils at all which may indicate a leak?
The high and low pressures of the sealed system will need to be checked by a licensed refrigerator repairer (at least here it does due to government environmental regulations regarding the handling of refrigerants) to find out what and where the problem may be.