I am assuming that there is 12 volt power going to the fridge with no fuses blown etc.
A common problem is with a fridge of that age is the heating element breaks or wears out.
A 12 volt fridge works by heating the gas up to a high temperature and as the gas is circulated around the fridge it draws heat from the fridge contents to cool down. This drawing of heat is in fact the cooling principle, it is a hard thing to get your head around use heat to cool down.
I reckon that the heating element is gone and I think that they about €100 fitted. As to where to go for a replacement, I don't know. A new fridge would start north of a €1000.
Best of luck