installing ubunti on a netbook does not work

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http://askubuntu.com – trying to install ubuntu on a external usb 3 500gyg harddrive for a netbook acer amd c-60 1ghz with 4 gyg or ram 64 bits on windows 7 no2. When i install the iso with the universal usb installer and dowloaded the ubuntu-12.04.1-alternate-amd64 iso file. When i reboot on the external hard drive, i have the language selection, then the menu...I choose to install ...and I get a black flickering screen. and nothing more. Any suggestion? (HowTos)