Can't login after setting up FileVault
It sounds like something broke, as the description sounds like you're unlocking the disk but then the OS is running a disk check (that's the bar) and failing (that's why the machine shuts off.)

One thing you may want to try is booting to Apple's Internet Recovery and using the tools available there.

To boot to Internet Recovery:


Start up your Mac and hold down Command-Option-R on your keyboard.
You should see a gray screen with an animated globe appear. It should say something like “Starting Internet Recovery. This may take a while.” 




Once booted to Internet Recovery, you should see the Recovery interface.



From there, you use the methods described in the links below to unlock or decrypt your FileVault 2 encrypted Mac:

Using Disk Utility to unlock or decrypt your FileVault 2-encrypted boot drive

Unlock or decrypt your FileVault 2-encrypted boot drive from the command line