I try to play and it wont work. It crashes when i try to load a world

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
Minecraft starts up and shows update notes. I click play and select a world and play.
What actually happened was...:
Describe what happened here
I start it up and it has a blank screen. I click play offline and select a world and when it tries to load the game crashes.
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...click load world with a world selected
3. ...