The game crashes when i try to open or create a world

Put the summary of the bug you're having here
The game crashes when i open or create a world.
What I expected to happen was...:
The game to create my new world

What actually happened was...:
Game crashes when its loading and building terrain

Steps to Reproduce:
1. log into minecraft
2. open a world(or create, doesn't matter)
3. then it crashes