You MUST have a working USB Diag key and of course your ekey7.
And you need to have the AVP OS loader on a fat32 formatted flash drive.
Plug in both the ekey and Diag key into the protected USB ports behind the metal cover and power on.
The AVP will always boot from USB if it detects the ekey and a valid bootable USB drive plugged in (the diag key). The diag key has it's own OS, so the AVP hard drive can be all messed up and it doesn't matter. Now if you plugged your Diag key into a PC newer than Win7, well you probably messed it up. You should NEVER put a diag key into a PC, there's no reason to.
There is a .bat file that will clean files that Windows newer than Win7 automatically writes to any USB drive you plug in that messes it up. But you'll need to run it on a Win7 computer to clean your diag key so it works again if it doesn't boot now from the diag key.
So as long as you diag key isn't messed up.
Plug in both the ekey and Diag key into the protected USB ports behind the metal cover and power on.
It will boot to diagnostics. And in diagnostics, select to clear Safe Storage, NVRAM, and the hard drive.
Takes about 15 sec and when complete, shut down the machine.
Remove the diag key and replace it with a fat32 formatted usb flash drive with just the OS loader on it, so you just have that and your ekey plugged in.
Power on, and it will install the OS to the AVP hard drive. When it completes, unplug the ekey and flash drive with the OS loader file on it and reboot.
System will initialize and put you into initial setup. Plug in your ekey and complete initial setup, there are youtube videos on how to do initial setup on an AVP.
When you complete that it will simply say "No Games Configured".
Now you can plug in your USB flash with games and go into the Manage Packages to install games, and then enable them. Don't boot again with the ekey in and a flash disk with loader files plugged in and your drive shouldn't do that authentication error junk again. Only install games after boot by plugging in your ekey, Manage Packages, and then plug in your USB with game loaders (also always on a fat32 formatted flash drive) to load them in and enable them.
That's it. Loading an AVP machine from blank. Will recover the system from pretty much anything if it really gets messed up. Just takes time to reload and configure games.
If your diag key is messed up and you have or can use a Win7 or earlier machine, PM me with your email and I can send you the .bat file that will clean the diag key of junk Windows files that mess up diag keys when they're plugged into a PC.