How can I fix my Servis M7262/6-S fridge freezer?

I bought this off ebay and was told by the seller that the thermostat had gone on it. I have been told by a friend that it may not be that. Neither the fridge or freezer works. It plugs in and the light comes on inside but thats about it. I would just like to know what range of possible problems it could be. How much are these fridge freezers worth second hand? It is in very good condition so I am prepared to spend up to around £100 on repairs depending on this. I am clueless about applliances so any info would be much appreciated!