Installing Ubuntu 64bit on Acer netbook causes black screen.

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http://askubuntu.com – Trying to install Ubuntu on an external usb 3 500 Gb hard-drive. I am using an Acer netbook. the specs are: amd c-60 1ghz with 4 Gb ram. I have a 64 bits windows 7 no2 installed. I downloaded the ubuntu-12.04.1-alternate-amd64 ISO and used the universal usb installer to install the Ubuntu 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)