Our freezer and fridge have quit getting cold. This is the third time I have unplugged and defrosted the freezer section. The freezer in back has totally iced up. Something must be wrong but what?

We are in a rental and this is getting really old. The landlord doesnt care much and I'm not feeling like ponying up to fix their appliances. I guess a part might be worth it if it saves me from throwing out the food in the freezer every few weeks.