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
exit
reboot
Hope that works, because I have no idea about RAIDs.