I'm afraid, your hive died from CCD, caused by neonicotinoid poisoning.
The bees collect these systemic pesticides in summer with their forage, and then the colony dwindles away to next to nothing in the winter, the remainder of the bees dies from the cold.
Maybe it's only your strongest colony affected, as they might have discovered a contaminated food source too far away for the others to exploit.
Please try to identify the source of the toxin, it could be seed treated crops, pesticide trenched orchards or lawn treated parks and golf courses.
You might want to join the campaign to get these pesticides banned.