It will always crash my game when i launch a world and it wont go online for some reason when i have 5 whole bars of internet

Put the summary of the bug you're having here

What I expected to happen was...:
For my minecraft to launch one of my worlds AND it wont go online for some reason.

What actually happened was...:
My whole game crashed.

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