VNC not installing in ubuntu 12.04.5 LST

I am trying to install VNC server though putty, but it is not getting installed.

I have run following command to install

1. sudo apt-get install gnome-core


2. sudo apt-get install vnc4server


3. vncserver

I am getting the below error, what is causing this?

msfl@chanakyauat:~$ sudo apt-get install vnc4server
[sudo] password for msfl:   
Reading package lists... Done  
Building dependency tree  
Reading state information... Done  
The following extra packages will be installed:  
  libfontenc1 libfs6 libgl1-mesa-dri libgl1-mesa-glx libglapi-mesa libllvm3.0 libutempter0 libx11-xcb1 libxaw7 libxcb-glx0 libxcb-shape0 libxfont1 libxkbfile1 libxmu6 libxtst6
  libxv1 libxxf86dga1 libxxf86vm1 x11-apps x11-session-utils x11-utils x11-xfs-utils x11-xkb-utils x11-xserver-utils xbase-clients xbitmaps xfonts-base xfonts-encodings
  xfonts-utils xinit xterm  
Suggested packages:  
  libglide3 vnc-java mesa-utils nickle cairo-5c xorg-docs-core xfs xserver xfonts-cyrillic
The following NEW packages will be installed:
  libfontenc1 libfs6 libgl1-mesa-dri libgl1-mesa-glx libglapi-mesa libllvm3.0 libutempter0 libx11-xcb1 libxaw7 libxcb-glx0 libxcb-shape0 libxfont1 libxkbfile1 libxmu6 libxtst6
  libxv1 libxxf86dga1 libxxf86vm1 vnc4server x11-apps x11-session-utils x11-utils x11-xfs-utils x11-xkb-utils x11-xserver-utils xbase-clients xbitmaps xfonts-base
  xfonts-encodings xfonts-utils xinit xterm  
0 upgraded, 32 newly installed, 0 to remove and 83 not upgraded.
Need to get 22.3 MB of archives.  
After this operation, 62.7 MB of additional disk space will be used.
Do you want to continue [Y/n]? Y  
WARNING: The following packages cannot be authenticated!
  libglapi-mesa libx11-xcb1 libxcb-glx0 libxxf86vm1 libgl1-mesa-glx libllvm3.0 libxmu6 libxaw7 libxcb-shape0 libxkbfile1 libxtst6 libxv1 libfontenc1 libfs6 libgl1-mesa-dri
  libutempter0 libxfont1 libxxf86dga1 x11-apps x11-session-utils x11-utils x11-xfs-utils x11-xkb-utils x11-xserver-utils xinit xbase-clients vnc4server xbitmaps
  xfonts-encodings xfonts-utils xfonts-base xterm   
Install these packages without verification [y/N]? Y  
Err http://ift.tt/x7aQTN precise-updates/main libglapi-mesa amd64 8.0.4-0ubuntu0.7  
  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)  


Failed to fetch http://ift.tt/1y5evB0  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkLRQ  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5exZC  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkLRU  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5exZF  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkLRW  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5evB6  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkNcl  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5exZL  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8c  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5exZQ  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkNcn  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5evBc  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8e  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkNcr  Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5evBe  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8i  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5exZU  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkNcv  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5eyg8  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8m  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8o  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5eywG  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkM8q  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5eygd  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkNsN  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5eygh  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1yNkMoI  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
Failed to fetch http://ift.tt/1y5eywM  Something wicked happened resolving 'us.archive.ubuntu.com:http' (-5 - No address associated with hostname)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?    
msfl@chanakyauat:~$ vncserver        
No command 'vncserver' found, did you mean:   
 Command 'vnc4server' from package 'vnc4server' (universe)   
vncserver: command not found    
msfl@chanakyauat:~$    
msfl@chanakyauat:~$ vnc4server    
The program 'vnc4server' is currently not installed.  You can install it by typing:
sudo apt-get install vnc4server