Two out of three hives dead, can't tell what this is
Last year was my first year beekeeping, and my very strong hive was dead when I opened it for the first time this season today. I'm attaching a picture of the bottom screen of the hive. It looked like the bees died in place, and most fell to the bottom. What is all this yellowish white stuff?? The second picture is what the cells looked like. I thought maybe chalkbrood, but it doesn't seem to fit quite right. Someone said maybe the stuff was crystallized honey, and that maybe the bees froze... here in Kansas? The bottom of the hive had only the open wire screen, no bottom board... Did I do something wrong?
The second hive just had no bees inside, empty cells, but quite a few dead ones laying around the entrance. None of the yellowish stuff like the first hive.
The third hive seems to be doing fairly well.
Would appreciate any thoughts...
Can't seem to get pictures to attach.