It is actually a boot failure. Normally the kernel reads some config from the initrd (the bootloader loads initrd and passes it to the kernel - thanks dan) and then does a bunch of setup stuff, and then it mounts the actual root filesystem, and then switches to using that. In this case, the root filesystem has failed to mount.
Hardware failure is most likely the cause, but misconfiguration can also make this happen. Probably hardware though.
If its misconfiguration, an admin can reattempt to mount the root drive on /new_root, and then ctrl-d to get the init system to try again
ELI5: couldnt open C:/ drive
Edit: clarified what loads the initrd - as per dans comment.