Windows comes with a utility that can scan hard disks and attempt to recover bad sectors and errors with files. If your external hard drive has a file or directory that cannot be read due to being corrupted, you'll need to run this utility on the drive. If it is possible to fix the unreadable files, the utility will recover the sector and the file will be restored. Otherwise, the only option to fix disk corruption is to wipe the hard drive and reformat it. This process deletes all of the data on your drive, not just the corrupted files.
Connect your external hard drive to your computer. Once the drive appears in your drive list, right-click it. Select "Properties."
Click "Tools" on the window that appears.
Click "Check now." Check both "Automatically fix file system errors" and "Scan for and attempt recovery of bad sectors."
Select "Start" to begin the disk-checking process. Check the files after you have completed the scan to see if they are fixed.
Windows also provides a way to restore a file to a previous state. In the Explorer window, right-click on a file name and choose "Restore previous versions" to access this procedure. Put one or more file backup systems in place for your data. Examples include mirroring drives and online automatic backup services. Windows Live Mesh lets you sync folders between computers.
Before you reformat your hard drive, make sure your drive's data is backed up.