How did the system “suddenly shut down”? Was it a power failure?
If you have good backups of your data, then reinstall may the fastest way forward.
However, if you need to save something from the disk, you could start a terminal one way or another:
- virtual terminal
- boot with the USB installer stick and start a terminal program
On terminal, you can give commands to save any data you wish.
After saving your data to some external disk, you could try normal management commands like
- sudo pacman -Syyuu
- sudo pacman -S linux linux-lts
and see if they help anything. Maybe some other management commands could help, too.
But if they don’t help, I’d suggest reinstalling Antergos (unless someone has a better idea…).