Samsung SRL 609 fridge freezer?

hi there!

I have a samsung SRL609 fridge freezer, lately the top freezer is not cold as should be.i mean the meats and other stuff is not frozen. it is blowing cold air out but i think it is not cold enough. bottom half fridge seems ok! cold.first i thought it needs topping up with gas or something.it is about 5 yrs old now.but never had any problems with it...until now!
anybody out there have this problem with their Samsung SRL609??
any idea what is wrong with it?? could it be senors ??
please HELP...