Minecraft will not run.

Put the summary of the bug you're having here: Crash Reports. Minecraft not appearing.

What I expected to happen was...:
Describe what you thought should happen here: what I expected to happen was Minecraft to launch and I can play it!

What actually happened was...:
Describe what happened here: When I press the 'Play' button, the launcher disappears and re-appears with a crash report!

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ... It may be my fault but don't know why.
3. ... Get a new launcher, I think it might be because of the 1.3.1 Launcher