The guess about the MBR is most likely correct. Zero out the first 512 bytes of the physical disk to ensure that any old MBR data is gone, then perform your repartition/format/install/etc. The FDISK command has an /MBR flag that *ought* to do this, if memory serves. A bootable Knoppix CD could be a way to do this if you have no other tools; the command would be 'dd if=/dev/zero of=/dev/sda bs=512 count=1'. The target device name may vary depending on what Knoppix sees during boot.