Why is only the bottom part of my GE frige cool?

I have a G.E. refrigerator side-by-side w/dispenser in freezer door. The problem I am have is the freezer side is cool but, not cool enough for the ice maker to turn on. It is also collecting frost on the inside back wall of freezer and there is nothing against the back wall. The refrigerator is only cooling in the bottom half, the top have is not cooling or circulating any airflow. Could it be the damper or thermostat for temperature control on that side?
G.E. Refrigerator/Freezer w/icemaker
model # GSS20IEPJWW only 2 years old

beverlyawatson@yahoo.com
September 2007