i cannot go into any server and i cant go into my worlds

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
I expected to be playing my old world
What actually happened was...:
Describe what happened here
Suddenly the whole minecraft crashes
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...I opened Minecraft
3. ...I entered a world