Try starting from the Atari Hard Disk Utilities floppy with the <Alternate> key held down. I rather suspect that your hard drive booter has become corrupted (or the hard drive itself has failed).
Ataris have no CMOS equivalent since the OS is on ROM. One of the first things the OS will check for is the presence of a valid bootsector. Obviously, it isn't finding it. Using the floppy's version of the hard drive booter should let you access the hard drive (you might need to recreate the icon first) in order to reinstall the bootsector on the hard drive.
