my game keeps saying minecraft error faled to start

my game alwas saying ERROR AAAAAAAAHHHHHHH!!!!!!!

*What I expected to happen was my game to start
Describe what you thought should happen here

*What actually happened was the game keeps saying error
Describe what happened here

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