How to repair a Servis m7554-2ff frdge/freezer?

I have a Servis M7554-2FF frost free fridge freezer about 3 years old. A few weeks ago it developed the fault initially very noisy ( fan ran all of the time. The noise and the fan stopped as soon as either fridge or freezer's doors opened. The min, med and max lights flashing without affecting its function and performance.
Now the noise has stopped. Nothing happens except the interior light comes on.
Can any body help identify the fault and how to repair it?
Is it thermostat fault or the interior fan fault?
I have been told that repairing frost free appliance is dangerous. Is it?