you have a file index problem or a physical hard drive error. Some or all your files are recoverable. The hard disk itself should be junked after you have recovered the files.
I have had great success with a product from Ontrack - the current product is EasyRecovery Lite 6.1 - Individual Edition (Free) it is limited to recovering 25 files per session - you can start new sessions (takes up a lot of time) to get more files. Or you can buy the full version for $200.
check them out at www.ontrack.com
another product is R-Tools (it costs about 1/2 what Ontrack does) you can see it at http://www.data-recovery-software.net