That's pretty general. Can you provide more details and history?
o Have you ever used this drive on any machine before?
o Does the drive appear in Device Manager, and does it appear as an empty volume in Disk Manager?
o What kind of external connection does it use? USB 2.0, USB 3.0, FireWire, eSATA, carrier pigeons?
o If you have another external drive, or a thumb drive, will it work on the same external port on your computer? Or might the port be broken?
o If you have another computer, or a friend with one, can the drive be seen on the other machine?
o Does it require wall power? Does a power light come on? Does the drive make spinning noises? Screeching noises? Clicking noises?