ReadyNAS Pro 4 - Stuck in "booting" - Cannot enter boot mode

I was watching a movie last night that was stored on the NAS, when it seemingly crashed. Switched it off, then attempted to power back on to find it hangs on "booting"

Unfortunately, that was the worst thing you could have done.  Many who are used to Windows lock-ups make that mistake,  If you ever find yourself in this situation, first try to go into the admin GUI or use RAIDar to download the logs.

But having already re-booted, follow the instructions that StephenB​ has given you and we can see if we can get you back up and running.  It is highly unlikely that USB recovery is the direction you should be going.  And in some cases, that can actually make things worse.