After I have upgrade to ubuntu 12.04, two days ago, I can't enter. After enter my login the screen shows a message: The system chrashed, one apps actual or former have failed. an then the screen gets in black. Help me, please. Thank you.
A lot of people have the same problem.
You will need to delete the compiz and compiz-1 directories in your home .config directory and re-boot. The files will be re-created when you log on.
If you can't get a terminal session on your upgraded system, boot a live CD with Ubuntu and delete the compiz directories on your hard disk; then remove the CD and boot from the hard disk.