Hi there chacol,
It is possible that there is something physically wrong with the drive. In that case, you will not be able to recover the data using software tools.
Have you tried something simple as just attaching the drive with different cables to a different port?(even to a different system) It will not hurt to try that.
Apart from this, if the drive is recognized by BIOS but not Disk Management, I guess you can try some data recovery tool for DOS mode. There are quite a lot of threads on that in the forum.
Cheers,
D_Know_WD