On initial boot up, the server hangs on boot and won't complete the cycle. The screen displays "Non-OS disk" or "Non-Debian disk" inserted message.
The most common cause of this problem is that the server booted with either a USB or external hard drive attached. In this scenario the server is trying to boot off the external device and not on its on OS disk.
The fix is to remove the external device and do a cold reboot of the system. It should then wake up normally.