Diane,
I feel for you, it is really disheartening!!! Most of us have been there....
There are lots of different reasons they fail. Heavy mite load in the fall, failure to build up strong enough..weak going into winter, small clusters, queen failure, other diseases such as nosema, tracheal mites, mice, ...and don't forget human intervention (been there done that plenty :-x )
Unless you can identify something that it could be, you can just clean out the hives as best as you can and get ready for the new ones...
Rick
As to exact causes, we'd need a pretty detailed history of how you treated, how they were in the fall, what you see in the hive now, etc. Are they all in one cluster heads in the cells? is ther honey within 2 inches of the cluster? What size is the cluster? Were there any empty but well formed queen cells in there?
The way you mentioned "one hive still has honey" indicates that one hive didn't, and that could be a starvation case if they couldn't get up to the sugar board.