Comfy with the command line?
I'd try this, but don't blame me if the Mac crashes and burns.
Boot into single user mode
mount the file system as per instructions on the screen
use the rm
command to trash the following:
rm -rf /Library/Preferences/com.apple.loginwindow.plist
rm -rf /Library/Preferences/loginwindow.plist
Hope that works, because I have no idea about RAIDs.