Emerald :
can you hear the drive spinning up?
If he is looking under disk management he is using Windows. For both issues in this thread it is likely the drives need to have a volume created on them in disk part or any other program used to create volumes.
Run the command prompt
type in 'diskpart' and press enter
type list disk
select the disk you need to configure (eg. 'select disk 1', or whatever drive that is not listed in windows)
type in 'clean all' this process can take a considerable amount of time (a few hours in this case)
then type 'create system volume'
You can then manage the disk from disk management, the problem you are likely having now is without a volume defined on the drive windows cannot allocate space or identify partitions, thus as it has no partitions it won't show up. Generally this situation occurs when attempting to break RAID volumes, occasionally when the drive is from a previous OS with a unique non-standard configuration, but more often when the drive was purchased and the manufacturer (or reseller, if not purchased through retail first hand) did not configure the drive before selling it.