How to get Ubuntu installed, when my laptop restarts without installing?

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http://askubuntu.com – I'm trying to install Ubuntu from USB flash. So I boot from it and the install begins. It works until it ask me which type of instillation I want. I choose alongside with Windows 7 and then it the computer restarts and Windows 7 runs without Ubuntu being installed! I tried this installation several times and every time I get the same problem. How can I fix this problem and get Ubuntu to install? (HowTos)