Working on a server today via Remote Desktop, I accidentally turned ARD services off…which left me unable to get back in to turn them back on. Found this command that enables you to log onto the box via ssh and then as root, activate ARD again. This command will restart the ARD service giving access to anyone in the admin group. Once running, you can go in again via ARD and make sure everything’s right.
./kickstart -activate -configure -access -on -users admin -privs -all -restart -agent -menu
Apple has a tech note on the topic: