I really hate to contradict; but, really have a problem with the pervasive "knowledgebase" answers which are technically wrong....
The first rule of data recovery (fixing a bad hard drive ) is to STOP WRITING on it so we want a diagnostic which will confirm our suspicion. Any operation which writes reduces our chances of recovery. http://www.hdtune.com
has a noinstall, zipped version of their free HDTune utility. Plunk it on a flash drive (preferably on another computer), unzip it, run it on the suspect system, then check the Health tab before doing an error scan. Reallocated Sectors (Health tab ) or more than two red boxes in the error scan identify the drive as failing.
Get another drive to replace the failing one. (Must be more sectors than the original; but, not more than 128GB if the original is smaller or it won't boot when you're done!)
then get Roadkill's Rawcopy ( http://www.roadkil.net/program.php?ProgramID=22
Unplug your CD, plug the cables into the new drive, use Rawcopy to copy the drive, switch the new drive where the old one was physically, plug the CD back in, and voila; the bad drive has ben replaced and problem solved.....
Rawcopy WILL continue after any "bad sectors" and replacing the failng hard drive solves that problem, too