Installed fedora can't access?

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http://forums.fedoraforum.org – I have intsalled f17 for many times by cd or usb stick. The install process is sccessful. But if I reboot my computer, it load win7 directly and I have no chance to boot into f17. As I readed the Installation Quick Start Guide, I find some difference. In the section of Boot Loader Configuration, I have clicked the "Change device " button and chosen /dev/sda3.But there is no Boot loader operating system list that I can configure the boot menu list. What's wrong? Thanks. My computer: Fujitsu LH531 I3-3250. 4G Ram, 320GB HD. win7 sda1 win7 boot sda2 win7 system sda3 f17 (HowTos)