Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Have you tried going to the partition tab in Disk Utility and then setting the Volume Scheme to 1 partition and then clicking partition?
 
Unless you have a physical write protect switch on the drive, or you have used some software to password protect the drive, then you probably have a dead drive on your hands.

What does the owner's manual say? Did the drive come with any software? Did you reformat it at one time?
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.