Minecraft crashes while being launched

Put the summary of the bug you're having here

What I expected to happen was...:
I expected minecraft to launch O.o

What actually happened was...:
Minecraft crashed.

Steps to Reproduce:
I just pressed "Play" then the mojang logo came up, then after a few seconds minecraft crashed. When I secondly launched Minecraft, it worked perfectly fine... I don't even know what was the problem :/