I would blame software rather than hardware. It could just be a windows USB issue, maybe driver related, maybe virus or spyware...
Could also be the external chipset issue, but I doubt that... since the external control chip really shouldn't go bad...
Are you trying to access the hdd and then your computer slows down? Then it might mean it's the hdd... the computers having trouble accessing it and is getting hanged up...
I have 7 external HDD's and I don't think this happens to me very often. However, I know I had a dead hdd once that wouldn't work, and when I plugged it into an external and plugged it into my comp, tried to access it, my comp went to hell... shrug...
GetDataBack is your friend.