Did you install the Windows 7 device drivers for your make and model. If not then go to the manufactures support web site and download the Windows 7 drivers to a folder on your PC and then start by installing the chipset/motherboard drivers, followed by the USB, SATA, LAN, Audio and all remaining drivers.
Also check the Graphics card manufacture's download site for the most recent Windows 7 drivers for your card.
ATI: http://support.amd.com/us/gpudownload/Pages/index.aspx
NVIDIA: http://www.nvidia.com/Download/index5.aspx?lang=en-us
JS
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