Sounds like a failing/failed hard drive. Test the drive with smart-tools and the manufactorers testing tools. Most offer a live CD for download.
An easy way is to use SystemRescueCD and fsarchiver.
link fsarchiver copies/restores on the file level, and handles per file corruptions. Rather than a big tar-ball that won't handle single file corruptions.
I recently had to do this with an old failing 20gb IDE drive. Attempted the tar-gzip entire mount point from the Slackware install disc. This failed because of some file corruptions. Fsarchiver was able to backup, and then later restore to a new hard disk. I was lucky because the only
bad files where located in /usr/share and /usr/doc. I made note of which files had problems and reinstalled these apps.
Run your file system's fsck on the drive before you backup. If there is any corruption, this might fix some of it. To restore to a new hard drive, boot with SystemRescueCD using fsarchiver to restore the partition. You'll have to chroot into the new hard disk to reinstall lilo.
If you don't want a complete backup/restore of everything, mount your hard disk from a live cd, and tar-gzip the files/directories you want.