samsung fridge/freezer model no rl39wbns

Please can anyone help me to figure out what do the letters rd flashing mean on my fridge/freezer.It began making a tinny bubbling noise at the back this morning and now is not working.I turned it off from the mains this morning and then turned it back on but it only stays on for about 20 seconds and then begins to flash continously the letters rd.My food is all beginning to melt.This fridge freezer is less than 3 years old.Thanks to anyone who can help me figure out what to do.