First of all some background: A hard drive is never supposed to show up. Partitions on a hard drive usually show up though.
Which yields the first thing to check: Are there any partitions on it?
You can check this easily via
- Right click
- Look for
Disk management under the header
If the HDD is new you might need to add a partition table and partitions.
If it is not new and contains FAT/NTFS partitions then check if they have drive letters assigned to them. You can do this by right clicking on the drive and selecting
Change drive letters and paths
If this do not work then put the drive directly into a computer. (After all, the drive itself can be broken.)