with a modern HD, if window's CHKDSK command reports bad sectors/clusters
then you have a problem - modern drives handle bad sectors internally, and
ONLY report them to windows if they run out of spare sectors (of which
there are typically hundreds) - an indication the drive is failing. backup
and replace the drive ASAP.
If the drive is SMART compatable (IDE, but not newer SATAs), the maker
probably has a SMART util that can tell you the drive's status, and if it
has run out of spares.