when i log on to my launcher or when i get to the real minecraft it crashes and goes away

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
i thought it was just a little crash and i could just get back on
What actually happened was...:
Describe what happened here
when i try logging on my minecraft it crashes and goes away and wont stop
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...