Chromebook usb recovery is not working.

My Chromebook froze while surfing on the internet. After minutes of not reacting I manually shut it down. After restart the Error: Chrome is missing or damaged I followed the instructions on the google website and called Google staff.

Now, having finally downloaded the recovery on my USB stick, I plugged it in and the Chromebook turned black. After a little while it tried to verify the stick. After some waiting again, another error occurred: un unexpected fault.

I tried that with 2 other sticks but its still not working. I tried to backup the laptop by pressing the round arrow and on/off. Not working.

Has someone any idea what else I could try?