If you turn off VNC / ARD on your hosted Mac by mistake, you can re-enable it thru a console connection via SSH (which MacStadium turns on by default on all rented Mac servers) with these instructions:
ssh 192.168.1.200, where the number sequence is the IP of your hosted Mac.
mypasswd, insert your desired VNC Password):
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -access -on -clientopts -setvnclegacy -vnclegacy yes -clientopts -setvncpw -vncpw mypasswd -restart -agent -privs -all
You can now close your terminal/SSH window, and attempt to re-connect via your VNC / ARD client as normal.