Your partition table or root directory got damaged. If the recovery programs can't repair them you have to write the files to another disk then reformat the hard drive. Same thing happened to me. My 500 GB drive was partitioned, so the not read portion was 3 out of 8 partitions. Mine was caused by using it on a slow computer. I rebooted not realizing that it had not completed reading the disk structure.
The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Compnet Ventures, LLC hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.