I started up minecraft (no mods, no nothing) and played on a world. But what I realized was that all the water had the wrong texture!!! Using one texture pack, it was pink with black squares and with the default texture pack, it had another texture packs water texture! The same thing happened on all my other worlds (regardless of what gamemode i was in). I closed minecraft, and started it again, but the same thing happened. And then, I relized that when I changed to the default texture pack, Minecraft crashed.