If the original DMS does not work then it got damaged somehow.
Either the partition data is damaged or the signature was destroyed (you put the wrong cartridge in at the wrong time, and wrote trash to the signature blocks!)
You can try to repair it using the utility (the boot screen or ALT+F3 - two options that both do the same sort of thing) from the repair/hack CD, or you can use the tool in PMM that does the same general thing.
If the partition data got damaged that will fix it. However, if the signature has been corrupted or destroyed then it will not.
If the signature on the original DMS drive got overwritten then you need someone with a valid signature file to put back on it, or a valid DMS you can copy it from. That will NOT make the DMS "blessed" again, but it will make it work with a "hacked" Phatbox.
In any event if you have a hacked box then the DMS is recoverable (assuming the disk itself is physically ok) as a DMS that will work in a hacked unit. However, if the signature is damaged there is no way (other than sending it back to Phatbox and paying whatever they want to "re-bless" it) to get back to where the DMS will work in a NON-hacked unit.