I don't think you've got many options here from a troubleshooting perspective. If the computer isn't picking up the device at all, there isn't much you can do other then send it to a data recovery service.
Maybe someone else will have other suggestions, but if the machine doesn't detect the drive at all no program is going to be able to recover the data.
http://www.drivesaversdatarecovery.com/
That's a pretty well known data recovery company.