Why did my freezer stop freezing after being unplugged for several days?
Freezers are not really designed to freeze things (at least not an entire freezer full of unfrozen things), they're designed to keep things frozen.  They're also designed to work with stuff in them, and will likely not be as effective when empty.

From your question, it sounds like you're running an empty freezer, and waiting for it to get cold.  This will likely never happen.   Put some frozen stuff in there, and monitor it for a bit to insure it's keeping the stuff frozen.  If it is, put the rest of the stuff in. If not, you'll have to investigate further.