Open a terminal and type following command to enable the remote desktop:

$ gconftool-2 -s -t bool /desktop/gnome/remote_access/enabled true

To disable the “Ask for Confirmation” dialog

$ gconftool-2 -s -t bool /desktop/gnome/remote_access/prompt_enabled false

If you check

System -> Preferences -> Remote Desktop

you will see that it is now turned ON.

You can turn it back OFF again from the command line using this command:

$ gconftool-2 -s -t bool /desktop/gnome/remote_access/enabled false

Now login to your Linux system from SSH & by using above commands, enable or disable the remote desktop.

Once you do that, you can use VNC Viewer from the remote machine to access the gui of your linux system.