Sometimes it happens that, due to some physical damage on the surface of the rotating magnetic disk inside of the harddisk drive, a bad sector occurs. Such a bad sector is commonly found by disk checking tools like "CHKDSK" or "SCANDISK" on Microsoft systems. This could also be indicated by listening to drives operational "sound". If you can hear some loud and unusual "clicks" during operation, the harddrive could be probably seriously defective and you should try to backup your data as soon as possible.
A bad sector itself cannot be repaired but there are usually many spare sectors in modern harddrive to compensate the sector loss caused trough the defective sector on the harddrive. There are various tools which can read the "SMART" (Self-Monitoring, Analysis, and Reporting Technology) information of the harddrive to predict such harddrive errors.
To learn more about bad sectors and the "SMART" technology, visit the following links:
In some cases the bad sector can be "repaired" with the help of windows internal tools by performing the following steps:
1. Double-click on "my computer" to open the my computer window.
2. Select the disk that you want to diagnose and repair.
3. Choose "properties" from the file menu. You should see the properties window for the drive that you selected.
4. Choose the "tools" tab.
5. Click the "check now" button under error checking status.
6. Depending on your version of Windows, choose either "thorough", "scan for and attempt recovery of bad sectors" or "scan drive".
7. Click on "Start". The tools will attempt to repair the bad sectors, if possible.
Should the repair attempt to fail then refer to the website of the harddrive manufacturer. Most of them have their own tools to check and fix the harddrive.
If this attempt fixing the harddrive also fails then contact the nearest available authorised service partner in your country for a harddrive replacement.