User /System Permissions none.(Set to 000)
Boot into single user mode (hold ⌘S on boot), then enter:

mount -uw /
chown root /
chmod 1775 /
exit


This will reset the permissions for the entire drive and all its contents allowing full read and write, and may take a long time — don't interrupt it. Once you are booted back in, go to Disk Utility and do a permissions repair to set the permissions correctly per OS X.