it just was loading the world when it just crashed

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
what i expected to happen was for the world to load well and end up running smoothly
What actually happened was...:
Describe what happened here
what actually happened was that when the world was loading it crashed, an this happens all the time now
Steps to Reproduce:
1. start minecraft
2. go to single player
3. select which world you want to go in
4. it loads the world then it crashes