Hi mejtalbot,
There are many reasons why your fridge is malfunctioning, however one of the most commonest is that the thermostat has packed up.
These are inexpensive to replace yourself, but once again you must know what you are doing. By shorting out the two wires at the thermostat the fridge should start working, i.e. if your thermostat is faulty. You would then have to replace the faulty unit.
There is no need to replace it with a Zanussi one there are numerous other universal ones that are equally as good
Regards