Recently I came across an unresponsive Chromebook that need recovering. I tried using the Chromebook recovery utility but it would always get stuck on step 3 at 0% on the final stage which is writing. Switching computers solved the problem but that is not possible for most people so I tried and succeeded using Rufus which is a piece of software that creates bootable USB flash drives. I also tried the Chromebook recovery utility a couple of weeks later and it decided to work. For a hassle free experience just use Rufus.