USB Device Could Not be recognized

When I connect the External Hard Drive to my computer, it says "Unrecognized USB Device". Sometimes, I also get errors like, "the USB Device is not recognized". But by disconnecting it and re-connecting, it solves the problem.
I don’t feel that this would be possible to me all the time, spending time by unplugging and reconnecting, to make it function properly. So here, I am really looking for someone, who can help me out with a solution for this problem.
