I do not see a problem with fdisk's hdb1 so problem might be in the Volume Boot Record.
In a root console run TESTDISK , if it is the VBR it will be fixed. If you do not have Knoppix latest version, testdisk may not work. More help useing testdisk is at http://www.cgsecurity.org/index.html?testdisk.html
At one of testdisk's screeens you can hilight the partition and use 'p' to do a directory listing.