If its in warrantee call Samsung out. I had the same problem, mine was out of warrantee and due to lack of money to call out an engineer I did some research and prodding and poking. The problem was traced to the fan mechanism that has iced up and is no longer able to move the cold air to the top half of the fridge. The same problem applys to the freezer compartment.
Solution, if it's stopped working entirely the following may not work. However if you can hear a ticking noise when the fridge / freezer is cooling - which is caused by the fan blades knocking against ice - be brave and get a screwdriver and after removing all shelves undo all screws to remove the back panel. From memory there less than 10 screws and a few clips. Once removed you will clearly see the problem. Ice. This blocks the airflow to the top half and blocks the drain. To cure the problem - until it ices up again - take a hair dryer to the ice and melt it away. Check it thoroughly for more ice. Alternatively empty the fridge and freezer turn it off and wait for the ice to melt. This will take a few days to melt completely. I hope this helps you.
Alan
April 2008