Minecraft never actually fully loads.

I have been playing Minecraft for a long time now and have never seen any bug like this.
Let me start off, the day before yesterday I was playing Minecraft for a long time, no bug seemed to have appeared whatsoever. Then, just yesterday, as I opened Minecraft, the loading screen never actually completes, it goes on and then stops at the last bar. I haven't tried deleting the game because I have a precious survival world on my account. I have, though, tried Shutting down and resetting my settings, none of which seemed to work.
Please fix this Mojang, I don't like paying for a game I can't play.