Clicking play on the launcher, green bar fills up from left to right but nothing happens

I have downloaded the launcher for minecraft and logged in. When I click play the green bar fills up from left to right. When it reaches the end, nothing happens. Nothing whatsoever.

What I expected to happen was...:
I was hoping the game would run and what may happen when should run would happen and hopefully played the game.
What actually happened was...:
What actually happened was that it was loading but nothing actually happened during the few seconds. Nothing happened after the green loading bar disappeared...

Steps to Reproduce:
1. Load up the launcher
2. Click the play button on the bottom of the launcher screen.
3. Loading bar fills up, but nothing happens