You might want to give us a little more background on what was done or what took place before the hard drive went AWOL. Otherwise, it's pretty hard to tell since it could be a number of things.
Does the HD make any weird noises, like clicking or a constant "winding up" sound? If so, then the hard drive is basically toast. You're going to have yo buy a new one for that PowerBook. If it's still under warranty, contact Apple for replacement parts.
Not that this would help, but it's worth a shot. If that PowerBook has OS X, boot into Single User Mode by holding down Apple-S after the Mac startup chime. Hold it down until you see text flying across the screen. Once at the command prompt, type the following:
/sbin/fsck -yf <hit the Return key>
Report back with results.