sorry phil when I said new I have had the freezer just over 1 year. it had worked fine. no controls had been altered,door was not ajar,no power cut,my wife said when she opened the door it was not cool air but warm air.
I could ask you lots of questions and diagnose the fault, but probably easier if you go to the following webpage, and it will help you to diagnose where the problem is, you will need to switch it back on to see what happens now, could be if all is okay now that it was just iced up and needed a defrost to clear the ice, also if it works normally for just a couple of hours then fails again, it's probably a compressor problem (may just need re-gassing)
http://www.ukwhitegoods.co.uk/help/fix-it-yourself/refrigeration-self-help/3713-fridge-freezer-fault-diagnosis-tool.html be patient the page takes a while to load.
Best Regards Phil