yea, ive had that prob before, from my experences it indicates that somethign is wrong with the hard drive chain somewhere. check cable conections (hard disk and mobo) replace cables if that doesnt work, and if putting a known-to-be-good cable in there doesnt work, than take the hard drive out and put it into another comp, see if it will work in another computer.. if it does, i dont know what to tell ya... experment.
when it happened to me, the controller chip on my hard disk died, i beleve. the bios saw the drive fine and everyting, it jsut wouldnt boot with the drive on there. i removed it, and it worked fine.
goof luck,
Jason