If it is the Thetford N175 it could be the glass fuse on the mains control board (at back of fridge and about 4 screws to undo it (T10 torx driver needed). Could also be no power to fridge - check 230/240 volt supply as it may be suffering from voltage drop as happens on some sites. Other possibilities include failed heating element or control board. As to resolving the problem it is probably best left to a workshop to do especially if you need parts or have little knowledge of mains electric work
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Have a look in the cupboards nearby for a switch that might have been knocked off. I turned the switch that the previous owner said was for the cooker off on mine and the fridge went off. Unsurprisingly it didn't turn the cooker off.
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