Are you sure the Xubuntu desktop is starting properly?
Do the following:
1.) Install pacakge "vncserver" on the machine you want to control. From a terminal, this is:
2.) Edit the file ~/.vnc/xinitrc, to contain:
sudo apt-get install vncserver
To edit the file, enter:
Or alternatively browse to the file and right click->Open.
3.) On the machine from which you want to control the other machine, ensure you have an ssh client installed. For Windows this can be "Putty", it should be installed by default on Ubuntu.
4.) On the machine from which you want to control, make sure you have a VNC client installed. For Windows this may be "UltraVNC". There's several clients on linux.
Now, this is how to get a remote GUI session up. It basically consists of logging in via SSH, then starting the VNC server, then connecting to it with a VNC client:
1.) SSH into the machine you want to remote control with VNC. Enter:
Enter the password when prompted
2.) Start a VNC Server instance. Enter:
The computer should print something like:
3.) Now VNC to the remote machine. For clients (such as Ultravnc on windows) who require it, remember to include the ":1" in the display address.
New 'remote-machine:1 (username)' desktop is remote-machine:1
This should work, to bring up a full desktop via VNC.
Alternatively, why don't you just install NX from NoMachine? Works a charm. Install server on the server, install the client on the client, and voila. Better remote desktop sessions than VNC.