failed to restart after installation

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http://askubuntu.com – I'm trying to install a 64 bits ubuntu desktop 12.10 to my new asus g75vw from a dvd. Everything worked slowly but fine until it finished, then the installation program prompted me to restart.I clicked restart button after which the computer freezes and finally I have to power it off. Now I can only boot into windows 7 not grub. Where did I go wrong and how do i fix it? (HowTos)