I saw that. But I asked you what type is your external harddrive - 2.5"or 3.5"model?
Also you still don`t even said is your pc desktop based or laptop?
And I understand that usb port works, but did you try the other ones to test if they will cause same thing?
Btw win 7 got itself old as we talk, In case that you missed - windows 8 is on his way