Okay, do you hear the fan in the back of the freezer running?
Okay, what it sounds like to me is your cold control has gone bad. It runs from the fridge temperature control knob to the damper where it checks the temperature of the fridge. If this goes bad it will either never let your compressor to turn on or your compressor runs all the time. The symptom of "frosty buildup" is a key indicator of the cold control on all the time. You need to replace that. I am sending you a diagram to show you where in your fridge your cold control is located. On the diagram it is #3. The part should run around $30.