my game keeps on crahing everytime i try to load it just crashes

Put the summary of the bug you're having here

What I expected to happen was...: i log in and play the game
Describe what you thought should happen here i thought i should just send the error to mojang

What actually happened was...: my game crashed
Describe what happened here i logged in and then the game frose

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...?
3. ...?