What you will find is that the back of the frezer has iced up, stopping the flow of air to the fridge. You will have to turn it off for 24 hours with the door open to allow it to defrost, or after turning it off, carefully remove the freezer back panel and defrost it manually. To do this remove all the baskets, swivel the ends of the runners so they come off, then release the tabs on the back panel righthand side and top to ease it out. There is a fan conected to the back panel. The connector is behind the small round thing in the back panel. Remove all the panels and you should see the cooling element. Use a hairdryer to defrost it in about 30 mins.
The usual reason it frosted up is that a door was left ajar.
Hope this helps.
Kintara
February 2009