Hi Joy, and Welcome to Tom's Hardware!
Is this a secondary HDD used for data, and not the operating system?
Until you find out exactly what the problem is, DON'T format or partition it, or write any data to it.
With it connected to your computer, go to Disk Management (right click on My Computer, Manage, Computer Management. In the lower left area click on Disk Management).
Could you please upload a screenshot of this Disk Management dialog box (use Photobucket or ImageShack)(copy & paste the forums url - usually starts with Img) to your post here, so we can see exactly what has gone wrong, and how best to correct it.