if all the food is still frozen at the top of the freezer cabinet and you have not set the thermostat to high then you have got air entering the freezer by way of the door seal as it seems it is not closing properly and this is probably because there is most probably a split in the door seal but check door is not warped. if food is not freezing at thermosta 2/3 then refrigerant is leaking and you need it looking at or a new one, it will cost about £120+ish to have it done so you can decide to have it done or get a new one
Denis (Moore Appliances), October 2006