Firmware defect BRICKS Seagate drives
A defective firmware in many 500GB+ drives is causing many drive failures too. Seems Seagate initially washed their hands of it and simply provided a firmware update for owners to apply BEFORE they hit the problem and left those with the bricked drives high and dry. But now they are provide a free re-flashing service through their data recovery arm.
Search the net for "7200.11 SD15"