Do I need to ask? What the heck, I'll ask.
Have you confirmed the problem isn't in the wiring or connector to that
particular drive? That is, have you check for proper voltage with a meter
or plugged in a different drive on that connector? Also, if you've
disconnected and reconnected the drive a number of times, the solder
joints on the drive's power connector could need reworking. Check the
obvious stuff first before jumping into swapping boards.
Of course, if you've already done those checks, you'll have to either
troubleshoot the drive to the component level (and then find replacement
parts) or start swapping boards. One word of caution on this, though.
Don't assume that just any board from the same model drive will work.
Sometimes they do, but often the drive's firmware won't be an identical
match and the swapped board either won't work right or may even cause
damage. For example, here's someone selling boards for your drive; note
their warning:
http://cgi.ebay.com/PCB-boards-for-...ryZ64460QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Then again, the prob may not be the board. It could be other things, such
as a bad platter motor, though that's less likely.