Dealing with a dead/dying colony is worst thing in beekeeping Fiona. Sorry its happened to you. Its not that common to lose a colony at this point in my experience because it has been relatively benign weather, certainly on the east coast. This suggests a problem that maybe developed several weeks ago. It would be useful if you could get an experienced beekeeper to have a look through the colony with you to see if anything is evident. If there is sealed brood then maybe chilling played a part - if no sealed brood then maybe the Q disappeared or did not mate properly. Did wasps take a toll on the bees? Questions to consider : Are there capped drone cells present? Are there cells of sealed stores present? where in relation to the bees? Are there lots of bees with heads stuck down into the cell or are they all on the floor? It is possible that the bees you saw flying recently were robbers.

If you can get a mentor to look in with you they may also be able to give you some guidance about how to clean up and sterilise and what to re-use.