Game freezes on "Launching"

Put the summary of the bug you're having here

What I expected to happen was...:
After the download has completed the game is supposed to launch so that I can play.

What actually happened was...:
It runs through the download function and freezes on "Launching".

Steps to Reproduce:
1. Click on the shortcut to launch Mincraft.
2. ...Select "Play" and wait for game to start.
3. ...