Can you post the model number please.
Ok what you need to do is empty the fridge and from there remove the plastic back panel one section at a time from the bottom upwards. It doesn't matter about the fan at the very top you can leave that section in still.
From there you will see the evaporator its the big silver thing running up the back. Have a look at this and see if theres any ice or frost on there. It should have a covering of frost all the way up.
Is this all blocked with ice at the bottom or is it just the bottom section that has a covering of frost on it?
Sorry for the delay in getting back to you. I did send a reply but it looks like it didn't go through.
As theres little frost on there and its just a bit at the bottom then you have a system fault. Either the compressor or a blocked evaporator as the evaporators do block up on this model as I have replaced quite a few of these.
Im afraid this isn't a diy fix as you will need to get a fridge engineer in as they will need to put there gauges on the pipe work at the back to see what pressure the compressor is pumping at.
Sorry this isn't good news but if you need anymore info just get back to me.