Let me set the scene: I get on my computer one day, I look at the Minecraft launcher, BAM. 1.9 is out. I fall out of my chair because I'm so excited. I launch the game, get on Minecraft. Menu screen is fine, single player screen is fine, multiplayer screen is fine. So I load up a world to see the new stuff. I load up the world and... no blocks. It's nothing but random sounds and textures that change as you look around and move. What do I do?