when you are getting bad sectors your harddisk IS already dead.
modern drives have dedicated areas (cylinders) where they store data of "bad" blocks.
means when the disk needs more than X (some hardcoded value) retries to read the data of one block, it "maps" the data to the reserved space.
the chances for a block to fail immediately and completely, so that the disk cannot read it at all are minimal.
if scandisk or any similar program reports bad sectors, it usually means that the reserved space for mapping bad sectors is full, or the disk has gone SO bad, that it cannot read the data anymore, even after some 100 retries.
so, if your drive shows only 1 damn bad block, replace it immediately!