There are always dead bees around a hive. What is "a lot"? Piles of dead bees is usually pesticides. A lot of crawling "K" wing bees is usually Tracheal mites. Most other problems are either brood diseases, which won't be killing the bees, or Varroa mites which usually don't kill them until later but if they were really serious this time of year you'd see young fuzzy bees with shriveled wings.