Whirlpool Fridge not working?

I have a Whirlpool Fridge. I am afraid I don't know the particular model, as I can't find any indication of a model number on the fridge. It's a standing fridge / freezer, with two separate parts: below is the fridge and above is the freezer.

Without any specific reason the fridge is not working anymore. Actually it seems to work but there only grows some ice on the top back of the fridge, but no cooling. The freezer part seems fine.

Please advise.