How did you connect it to the computer (USB or Firewire) and does it show in your file manager is a removable device?
I recently added a USB SATA drive to my file server.
It came formatted for NTFS. My Debian did not have NTFS drivers (they are available for Debian, but are not default. Debian is rather aggressively free.)
fdisk -l could see the drive, but not the partition.
(I used GParted, which previous posters have mentioned, to repartition and reformat them. I second their recommendation. I posted a screen shot of GParted here