Linux on Lenovo Z575 - no display after installation

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http://unix.stackexchange.com – I am trying to install Linux on Lenovo Ideapad Z575 (AMD). When I run Ubuntu or Fedora from a LiveCD, I got some initial screens (purple screen with small icon for Ubuntu, some information screen from Fedora), and then.... nothing. For Ubuntu, I have a black screen, although I hear the Ubuntish sound when the login screen appears. So it is there, but the display does not work. Any ideas how to make the display working? (HowTos)