Chrome OS recovery not working (ACER C720P model PEPPY E8K-K7G-E7W)

Good day,

My Chromebook has the message 'Chrome OS is missing or damaged'.

The message appeared 2 days ago and I followed the instructions in making a recovery drive. It worked and everything was reloaded. Two hours later, however, it had a blank screen and said something was loading/processing and now the 'Chrome OS is missing or damaged' message is back, but when I try to use a recovery USB it loads and ends with 'an unexpected error occurred' and guides me to the Chrome website which guides me to do what I've just done. I've now tried 3 different USBs (each one twice) and the same message appears. I have tried it both by starting it straight up and by starting in recovery mode (esc+refresh+power) but the messages and the processes remain exactly the same. 

I've also tried entering developer mode with Ctrl+D  but no matter how long I leave it for, it ends with is the same Chrome OS error message. I've even tried using the recovery USB straight after, but to no avail. I end up restarting my Chromebook and it prompts me with a space bar to reinstate OS Verification.

When I press tab the error says 'no bootable storage device in system'. That error  message says 'recovery button pressed' when I start it up in recovery mode. I am at a loss as to what to do. My Chromebook wasn't jostled or mishandled before all this happened and has remained on the same stationary spot throughout. Additionally, the Chromebook was on, but not in use when all this occurred, so I don't know how this error arose in the first place.

Is there anything more I can do? I'm open to re-trying things I've done before.

Thank you for your time, have a lovely day.