When a disk "boots" it gets its instructions from firstly the firmware (PC board on the drive) and secondly from the microcode stored on (inaccessible to you) sectors on the disk.
There are known faults in some drives which make either of those two unreadable, therefore making the disk unreadable by BIOS/software.
Copy off what you need, and do it NOW if it is showing failure symptoms -- disks are so cheap these days...
Last edited by rustle; 6th May 2005 at 17:15.