Freezer doesn't work properly. Not cold enough

Freezer doesn't work properly. Not cold enough

My samsung upright refrigerator has the freezer in the bottom. It stopped working but the fridge part is working well. Actually the freezer becomes a fridge. Don't know why. We unplugged and kept it off for 24 hours, but problem still there. However, if we "power freeze", the freezer will work until we turn off "power freeze" button.