When the drives are installed the raid controller is reporting the Virtual Disk, which makes the system try to find the OS to hand off to, but when you remove them the controller is reporting there isn't an active Virtual Disk, so it passes on to the next device in the boot order, then when there isn't a boot device found it gives the error. This is all normal and should not be a concern.
Admittedly, I made a mistake. When attempting to reset the root password, I modified the boot line rather than the GRUB as intended. This has lead to me getting stuck in the scanning for devices on boot and I can no longer modify it because of this. I attempted to go through the BIOS boot manager to boot from Hard drive C: RAID PERC, but after selecting it the system freezes. Is there anything else I can do to fix my issue? Thank you
PowerEdge R520 Stuck on Scanning for Devices