Open windows command prompt
cd %programfiles%\winrar
At the command prompt type: unrar x c:\YourFile.rar /kb /v c:\files\
Done

Reference: 

http://club.myce.com/f3/winrar-extracting-corrupt-files-71185/

If you have corrupt rar files, try this reference: Some options for corrupt RAR files

http://www.afterdawn.com/guides/archive/some_options_for_corrupt_rar_files.cfm