my ubuntu won't start

What make and model system?
Which release?
What video chip do you use?

release 12.04
video chip: Nvidia

When you stuck at this state , try to hit CTRL+ALT+F1 and see if you can connect from there with your username & password.. then you have to memorize the commands below and give them one by one .. (or write them down to a paper)

sudo apt-get update
sudo apt-get dist-upgrade
sudo dpkg --configure -a
sudo apt-get install -f
sudo dpkg-reconfigure lightdm
sudo service lightdm stop
sudo service lightdm start

the last command will attempt to bring up the login screen , tell us if did it.

Thanks

no it didn't work
to of the command didn't work eithre:
1. sudo dpkg --configure -a
2.sudo service lightdm stop

Did you install the proprietary video driver yet?

it was working fine
and when the computer start i can see the the ubuntu screan "thinking" and the it gose to this screan
http://jpg.co.il/view/5103c2a585fa9.jpg/
but how do i install it?

its o.k. i figer it out
sudo apt-get purge nvidia-*
sudo rm /etc/X11/xorg.conf
sudo nvidia-xonfig
now its working good
thanks anyway