You should not need to buy a new disk, however the disk will need a 'reset' of the factory settings. You will need to contact Samsung and ask them for the PSID Revert Tool for the drive. That should restore the drive to factory state.
Samsung does not like giving out the tool, and I have had some customers report that they were instead asked to send the drive back to them, and were given a replacement. I have noticed the trend for this being for the 850 drives more than the 840's. They may not have a PSID Revert Tool for the 850 that is publicly accessible.