First make sure X server is installed - if startx command is not found, it probably isn't. In that case install it with:
sudo apt-get install xorg openbox
Replace openbox with the windows manager of your choice. You may also want to install xauth
and ubuntu-desktop
, but I'm not an expert in Ubuntu in particular.
Sidenote: I assume that this server is able to install software from Internet repositories. If it can't, you'll have to setup usable repositories, either on the Internet or on your Live CD.
If X server is installed but won't start, check /var/log/Xorg.log
for errors. Google those errors up and come back here if you don't find any solutions.