New Launcher hangs in "preparing" - GAME DOES NOT START

Put the summary of the bug you're having here

Updated Launcher (which was working a few hours ago) has now stopped working, after a forced update "adding runtime". The Launcher hangs in "preparing" after clicking on "play" but the game will not launch.

What I expected to happen was:
Minecraft Game to start after clicking on "Play".

What actually happened was:
Launcher hangs and the bar at the bottom says "Preparing", but nothing happens.

Steps to Reproduce:
1. Open Minecraft
2. Wait for Launcher to load
3. Click on "Play"
4. Wait forever and be very frustrated!

Please help!