What I should have said right at the beginning, but I have been a bit busy relocating the server etc...any hoo just in case this helps anyone else:-
The flashing question mark, in a folder, indicates that the Firmware cannot find a valid system folder. Resetting the PRAM or rebuilding the desktop will not generally help, but it is sometimes worth a go.
If you have a copy of "Disk Warrior", boot from the CD and rebuild the directories. This "almost" always works. If you have Norton's you can try it but it is not always as succesfull as "Diskwarrior".
In the event that "Disk Warrior" is not available, then a CLEAN install may be your best option. Another trick, is to boot from any bootable CD and explore the Hard Drive, if it is visible on the desktop. Open the HD and you should see the System Folder. It should have a Happy Mac icon on the folder. If it does not, open the folder and drag the finder out of the folder and then close the folder.
Drag the finder back into the System folder, without opening the folder, (or allowing it to open) and see if the Happy Mac icon reappears. If it does, try a reboot. This is called a 'blessed' system folder.
If the HD is not visible on the desktop when you boot from any bootable CD then you definitely have directory problems which will need to be addressed, preferably by Disk Warrior.
The worst case scenario is that the Hard Drive has failed!
This will give the same symptoms and the drive will NOT appear on the desktop when booted from a CD.
If you are not sure what you are doing, and the data on the disk is 'critical' ie 5000 digital pictures that are irreplaceable and not backed up, then I would suggest that you let a 'professional' have a look at it.
Most hard drives are recoverable as long as you have the right 'software' tools.
Regards
Ric