Centos – “Unable to open display ” “” error on VNC Server

I'm trying to run a GUI for my CentOS 6 server. I've installed VNC, and I have followed this guide through to the end – http://wiki.centos.org/HowTos/VNC-Server

Once the VNC server is started, I try to access it through the command:

vncviewer -via username@xxx.xxx.xxx.xx localhost:1

… just like the guide said. Once this runs, it asks for my password for the account, and then displays this error:

vncviewer: unable to open display ""

I've installed GNOME display as stated in the guide, by using the command:

yum groupinstall Desktop

Any ideas?

Edit:
I'm on the CentOS server in question, which looks like terminal at the moment.

I'm trying to get a GUI display running on it, I've entered the command after starting the server vncviewer -via user@ip localhost:1
but it resulted with the same error:

vncviewer: unable to open display ""

In my /etc/sysconfig/vncservers file, I have:

VNCSERVERS="1:user" 
VNCSERVERARGS[1]="-geometry 800x600 -localhost"

Output of netstat -plunt | grep 5901 :

tcp        0      0 127.0.0.1:5901       0.0.0.0:*    LISTEN      29577/Xvnc

Edit #2:
After installing the new packages and running 'startx', it ran for a while. I then recieved a few errors:

Fatal server error:
(EE) no screens found(EE)
Server terminated with error (1). Closing log file.

It looks like it created a log file of the error.
Forgot to mention: After this process errored, Putty encountered a fatal error, causing a connection abort.

Edit #3: Running the command 'init 5' seems to break my server. Had a 'connection error' after running it. Cannot connect back, going to have to get the admins to restart it from their side.