Hi everybody.
I'm not a Linux expert and I need help to understand what happened to my ubuntu.
I had 10.4 LTS version and upgraded to 12.10 release using update manager. Everything was good, no problems or errors during the upgrade.
I reboot my laptop, found a new grub system (normal thing, i have win7 too) that lead me to a new login page.
Login goes well, but then i see strange things. My desktop appear and disappear, sometimes there are icons on it, sometimes there's only the wallpaper. Sometimes the screen is covered by strange large images like smiles and stars. No application bar or cairo-dock appears. I can call the shell with the keyboard, but it appears and disappear with the desktop. I tried to write commands into it and it works, but when asks me for the sudo password i just can't type it correctly because of the lag.
I think this is a graphic problem but i have no idea how to fix it.
The only thing i can do is logout with ctrl+alt+canc and go back to the login screen, that is correctly displayed .

I thought that the cause was my laptop, since it's quite old. I have an AMD Turion 64X2 (1,60 Ghz) Processor, 2,50 GB RAM and a nvidia GeForce GO 6150 (125 MB) graphic card.

I tried the Lubuntu live cd to verify if it's an hardware problem. It's going the same. Instead of the desktop, I see horizontal lines, black screen and other stuff like this.

I really can't understand what is happening. I had no graphic problems before the upgrade.