Loading Issues with Packs

Hello, so I've been currently trying to play minecraft, and it won't load any of my packs, when I've already purchased these, and won't load any items to specifically edit the character. My world packs won't load either, and when it asks me to download the template, it loads the world but everything is missing, like the other characters. The enemies, fish, mouse, everything that should be alive is missing. You cant complete or play like this. Also, sometimes it tells me some of my worlds became corrupt, and therefore I have to delete it, as i cant do much other than that. If you could please help with this, I would really appreciate it. Thanks.