Symptoms : Black screen with Hangout logo, "ERROR_005" is displayed on the bottom of the screen.
Problem : The Chromebox's Chrome OS version is likely to be very outdated.
To force update to the latest version, you have to login on Chrome OS in desktop mode (CTRL+ALT+S at the starting screen when the Chromebox is rebooted)
Then you can access Chrome settings and proceed with a manual update.