Game Crashes In Under A Minute Of Playing

Put the summary of the bug you're having here

*What I expected to happen..."
Describe what you thought should happen here
Me joining the game and having no problems.
What actually happened was...:
Describe what happened here
I have lag. Also, my computer is crashing in under a minute of joining one of my worlds.
Steps to Reproduce:
1. Open the program and play.
2.Click single player mode.
3. Choose a world and in under a minute, the game crashes.