I recently installed mrchromebox UEFI firmware onto my Chromebook I haven’t been able to get any OS to work now I boot up my Chromebook it puts me into the UEFI shell I type exit then I can’t even choose a usb to boot on it just shuts off after like 15 seconds I have to mess with the charger and battery cable to even get it to post 
Someone please help me.
Maybe the Chromebook itself is faulty? When you turn it on, does the coreboot boot logo show? Have you tried pressing escape when the Chromebook is turned on? Also, what board name and brand is your Chromebook?
Yes the Coreboot logo pops up and I have tried reseating all the cables on the back but now the Chromebook won’t post at all the battery indicator lights up but no post. My board is zork and my Chromebook is a Lenovo 14e gen 2.
The default boot sequence is Installed OS (if you have, if not it won’t be in the chain) > USB/SD > EFI shell
It can be modified though.