You said the drive is not recognized at start-up, but does the BIOS still recognize it?
One of the better $60 I've spent, HDD re-generator:
HDD Regenerator - Dmitriy Primochenko Online It creates a bootable CD/DVD. Attach the ill drive and boot the system, and answer a few prompts then let the software do its thing. This can take hours, as it inspects every sector on the drive.
If...
IF... the drive is recognized at the hardware level (BIOS) and it's not making any abnormal clicking noises. Good chance the program will, make the drive readable as a slave (possibly bootable). Harvest everything you can and move it to a healthy, new drive.