Dissapearing HD

Hey guys, I need some help pertaining to dissapearing drives.  My friend's 10GB HD decided to dissapear from his computer, he's running WinXP service pack 2... and that's really all I know of his computer.

Anyway, besides the fact that the HD might have died on him what else could be the problem? Is there some kind of tool that'll search for the drive or something? :\

Never dealt with this before... Any help would be greatly appreciated!

Does it disappear from the BIOS setup screen?

Open the PC up and listen to the drive when you turn the pc on-does the drive spin up?

Did you add any other devices that draws power?

Also, check out the disk manager to see if it hasn't been detected, but not assigned a drive letter. (control panel->administritive tools->computer management, and then click disk manager).