Zanussi ZX79/5SI fridge compartment not cooling

Hi we have just started to have a problem with our fridge freezer.The freezer compatment seems normal but the fridge compatment is not cooling at all and the temp warning will keep sounding randomly i have quite good with fixing thing so have had a little look inside but have found this model very difficult to get into i removed the top part in the freezer section to have a look but found no excessive ice but the polistyrine was quite badly melted on to what looks like the cooling evaporator so decided not to touch it incase i bust the freezer aswell which is full of food would you think this is the source of the problem ? could not locate any of the fans or flaps to check them any help appriciated thanks nigel