GUI does not appear after installation

You must be connected to internet.

At boot try to go on a terminal by pressing CTRL+ALT+F2 make a login with your user and password then type:

sudo apt-get update; sudo apt-get upgrade
sudo --reinstall install ubuntu-desktop gdm xserver-xorg

give your user password when requested, you don't see nothing when you type it, then press enter.

sudo dpkg-reconfigure xserver-xorg

Please perform the little setup procedure then restarte the pc, type:

sudo reboot

Hope This Helps

but how to configure broadband internet connection from cui at localhost root

Please login and type:

sudo ifconfig -a

give your user password when requested, you don't see nothing when you type it, then press enter.

Please tell if you network card is already recognized by the system for example: eth0... and if it have already an assigned ip

Do you have a ethernet router...?

Thank you

If your router can lease ip (dhcp server) try to open (using one of this editors: nano, pico, mcedit )
this file:
sudo [nano or pico or mcedit] /etc/network/interfaces

My /etc/network/interfaces content

*------------------------------------------------------
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
*---------------------------------------------

Then edit the /etc/resolv.conf
and put the openDNSserver addresses:

nameserver 82.105.36.210
nameserver 208.67.222.222

save and exit and try to restart network:

sudo /etc/init.d/networking restart

Try to update your system, type:
sudo apt-get update
sudo apt-get upgrade

If you are still in trouble i think you must we must configure some other parameters or pppoeconf to configure your broadband access
to configure your pppoeconf simply type

pppoeconf

Hope this help