You've probably broken it, if it won't connect using every and any USB port on your PC then you need to break it open and use it as a slave drive, if this also fails then it's dead to the tune of $900 to get a lab to recover from it.
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DOING ANYTHING I HAVE SUGGESTED IS AT YOUR OWN RISK, NEITHER I NOR SEAGATE TAKE ANY RESPONSIBILITY, IT'S YOUR CHOICE TO DO WHAT YOU FEEL IS BEST FOR YOU
