[lubuntu] problem to install lubuntu quantal on vaio vpcyb1s1e

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http://ubuntuforums.org – Hello! I'm french user of lubuntu, sorry for my poor english. I try to install lubuntu quantal on sony vaio vpcyb1s1e. I can try lubuntu with usb-key. I can install lubuntu quantal. When it's finished, i reboot and lubuntu starts but stops in starter panel. perhaps a X pb? (lubuntu 12.04 works without problems) Thanks for your help. (Hardware)