Chances are your magnetic screwdriver did absolutely NOTHING to your HDD. You'd need a much bigger magnet than that to wreck anything. (remember that inside
the HDD are some huge
rare earth magnets used for head positioning that don't effect the data in the least)
Have you tried connecting the HD back to where it was originally?? This would be your first step.
If you somehow did
mess up your drive, I'd recommend Spinrite http://www.grc.com/sr/spinrite.htm
for recovering your data.