[Al Skierkiewicz]

Dave,
It is always possible that the internal HD connection or interface has failed. I would first look to see that everything is firmly connected. The powerbooks are easy to get into through the keyboard. With the power off and the battery removed if you can get it, remove the connector on the HD and reinsert it. Don't replace the keyboard just yet. Power on with the keyboard connector attached but out of the way and see if the drive is actually spinning. If not, you might try a little gentle shake or tap on the case to get it to spin up. Once up you can then get your date moved to another drive. If that doen't work, MAC in some models have power management through several autoresetting solid state breakers. These do fail from time to time.
If none of this works, you might try removing the drive and installing in an external USB drive carrier. Several computer stores carry these. I have one from MCM. Mount the drive in the external case, connect through the USB and see if you can get any data from it. If this doesn't work, you only bet will be to go through a data recovery service. Check with your IT department, some companies have internal people who specialize with this problem.