The problem you have is that the panel at the back of the fridge inside is clogged with ice,it could have a sensor,drain heater or defrost heater fault.All of these are replaceable at a lot less than replacing appliance.The best way to check if there is a fault is to hold top two buttons on display panel together for about 10 seconds,all digits should flash twice from memory,then an audible warning.Keep holding the buttons until the the panel goes blank(dont worry)this is going into self diagnosis stage,if any of the segments light up,then there is a fault.It will stay like this for about 20-30 seconds then return to normal.
MARK STEVENS, February 2009