[ubuntu] Installed Ubuntu but it doesn't boot without the installation source

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http://ubuntuforums.org – Hi, I installed Ubuntu 12.04.1 64-bit LTS beside my Win8 which is 64-bit, too from a memory flash drive. The problem is there is no such a list to select one of the installed operating systems. The computer itself runs Win8 automatically. If I want to go through my newly-installed Ubuntu, I HAD TO connect the flash drive to my case and manually select boot options, then select the flash drive to boot. After that GRUB will show up and I can choose one of the operating systems including Ubuntu. The point is, I cannot use my Ubuntu without my flash drive but as I said, I INSTALLED the Ubuntu stuf (Hardware)