ubuntu wont boot after installing wubi from windows 7

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http://askubuntu.com – I have installed ubuntu destop with the windows installer (in windows 7). The installation seemed to be fine. However when I restarted the notebook (hp pavilion g6) and choose to boot ubuntu, it only showed the violet screen and the logo and then it got a black frozen screen without doing anything. Windows 7 works fine. What should I do? Thanks!! (HowTos)