There are dead bees from old age, disease, starvation, or if you have honey in your hive, other bees want to come into your hive to steal the sugar, and they fight and kill the bees, and there should be dead bees outside of your hive, and you will see bees fighting. Under normal circumstances, bees will clean the inside of the box, if they do not clean, your bees have a problem, look carefully to see if there is a lack of sugar or bees are not sick.