how can I fix my refrigerator Diplomat, APP6302?

When the fridge is switched on the fan is working but the fridge is not cooling .... there is sometimes condensation formed on the inside of the back wall .... after a while the fan stops. This is an integrated Fridge which is less than 3 years old but the shop where I purchased it is no longer there (MFI). Can you help is it possibly the thermostat?