What operating systems are you using..
If it's Windows 2000 or XP, have you gone into drive management and formated the drive and assigned it a drive id? If it's not formated, you won't be able to see it other than perhaps in your BIOS on booting saying that it sees a Maxtor (WDxxx, or whatever brand drive it is and what device is it, (Primary Master, Slave, etc).