Importing the photos that have already been imported is never the answer.
Since you have stated that you copied the photos to the new HD (and they are in a folder of the same name), then you have to re-connect the photos inside of Lightroom. Find the folders on your old HD in your Lightroom Library Module (on the left, in the Folder Panel), and then use these instructions (scroll down to the section entitled "Updating Folder Location")
Thanks for this link.
LR is great at some things, but lousy at housekeeping. I will never ever use LR to move files.
It seems as if there should be more sites on the internet that warned of the foolishness of moving files with LR!
Moving files on the same drive is fine with LR. Moving them from an external to either another external or to your internal is something you should do with a File Manager program and then Point LR at them. Also Moving is a VERY BAD IDEA. You first COPY the files then once you are sure they are all copied correctly you Delete them from the old drive. Or format the old drive.