apt-cache policy xserver-xorg
. If it has installed correctly, then I don't know. However the absence of a gui could be the cause of your problem, and a problem installing xserver-xorg may be the reason.
If it isn't installed, then you could try as root
apt-get install xserver-xorg
but I suspect it won't work- otherwise it would have loaded when you installed your OS.
Inability to install a package with a tightly packaged distro eg Debian is because a dependency cannot be satisfied. To overcome this, you may be able to make a small change to your /etc/sources.list. Please post it. But, in some cases, it is necessary to do a clean install (e.g. when you have upgraded some packages by tweaking your sources.list to access testing or unstable repositories).
I have found Debian easy to clean install, provided you have your home directory in a separate partition. If it isn't happening, don't waste too much time trying to fix it.