Ubuntu installation does not respond after rebooting

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http://askubuntu.com – I installed Ubuntu and after completing the steps at the website and rebooting my computer shows a menu to choose between Ubuntu and windows 7. When I choose Ubuntu it shows that it is completing installation and a dialogue box appears which shows the status of "copying files..." and then after a few seconds it shows "almost finished copying files" and it remains like that. After this it does not shows any increment in the process so I assume that it is hanged. Please help. I already tried opening my windows 7 and it opened just fine. I need to complete my installation today because i need s (HowTos)