Clicking can also be a symptom of a bad controller board. It is possible to switch controllers on the drive (assuming this is an IDE/SATA) drive; however it has recently become more difficult to do it. Find an identical drive, remove the controller, you will need to swap firmware chips from the bad board to the good one which will require some good soldiering skills. You can then put the good controller onto the bad drive. I have seen this fix the "click of death" issue before, but it is by no means a guarantee. If this is truly critical data, contact a professional service.