What operating system are you using? If Windows 7, try right clicking on Computer -> Manage -> Disk Management. From there it should list all of the discs, even those that may not be formatted correctly. If you can see it there, then you may need to format the disc, which would destroy any data you had there.
You should also try looking to see if you can see the drive from the BIOS or another computer or even a live Linux distribution. If you can't, the disc may be corrupt or damaged.