I also had the 'Hell'o camera and 'detach screen' issues on my Surface Book. MS now have working patch process:
'Hello' stuck on 'Turning on camera' and 'Preparing security options'
Which states the following:
Step 1: As your Surface is powered on, press and hold the Power-button for 30 seconds.
Step 2: Press and hold the volume up-button and the power-button at the same time for at least 15 seconds, then release both.
The Surface logotype might flash on the screen while performing this step, but just keep both buttons pressed for the 15 seconds.
Step 3: Wait for about 10 seconds after you released the buttons.
Step 4: Start your Surface again by pressing and releasing the Power-button.
The UFEI is actually not a part of the troubleshooting. When you reach the UFEI setting, simply choose 'Exit' and 'Save & Restart' (you may only have the option to choose "Restart").
The 2-button shutdown is a troubleshooting step which searches the Surface for problems, and tries to automatically fix these, and it is really helpful if the problem is caused by drivers which are acting up or installed incorrectly.
Drivers are usually a reason for things that stop working suddenly, so you can use the 2-button shutdown in these cases.