shuts down and items go

when i open inventory, screen freeze. and i have to alt+F4 then reopen the game. when it opens, my inventory is empty. it repeats constantly. for instance, 7 times in an hour. i lost diamond enchanted items, and many more.when i get back to take the items where i died, they disappeared or disappear in front of my eyes thus i cant take back them. it is really irritating.