Try this;

http://kb.wisc.edu/helpdesk/page.php?id=5097

If this fails to resolve the problem, you could have permanently damaged sectors on the hard drive. Sometimes these are repairable (if only for a short period of time to allow you to back up the data from the damaged part of the hard drive)

To check for this, many Hard drive manufacturers will have a down-loadable utility such as the Western Digital Data Lifeguard Diagnostics/health check utility to burn to a bootable CD to check the hard drive health as the hard drive might be approaching the wrong end of the bathtub curve.