Any suggestions re 3rd-party disk utilities for an external hard drive with no bootable system?

When I plug in my external LaCie drive I get an error message "the disc you inserted was not readable by this computer."

The only options offered are "ignore" or "eject"

Disk Utility sees the disc but does not give a repair option.

Any suggestions re third-party disk utilities that will work on an external hard drive that has no bootable system??