Alesis HD 24 software

A little more information would be good.
The device is a device that records analog sounds on hard drive data files directly, yes?
Yours was working and now can't see the data that you had stored on the drive?
Our best approach to this would be to attach the hard drive to a computer's IDE port and see if Alesis chose to use a drive format that Windows supports. Or Linux. If that is the case, and the files can't be seen easily, a number of members can walk you through the process of scanning the drives for files.

In the meantime, I suggest that you
Contact Alesis for support
If the data is of great value to you, consider professional drive recovery services (think one to three thousand dollars)
Get a second drive. In the future, do frequent backups of your critical files. Alesis advertises that "Two hot-swappable media bays provide convenient access to recording drives and allow data backup in minutes. You can edit tracks internally or easily transfer to computer via an Ethernet connection." Backups are the only way to ensure long-term safety of data. Preferably backups kept in another building.