2nd Internal Hard Drive has stopped mounting on the desktop

Hi,
I just ran Cocktail, and now my 2nd internal HD won't mount on the desktop. There's just a bunch of backup files on it, no system software. Any idea what could be wrong or how I'd fix this?
Thanks,
Michael

Dead drive? Will it mount NOT in the desktop?

It was running fine until I ran Cocktail, then when the machine restarted, it didn't even mount on the desktop, and disk utilities doesn't see it, but here's the kicker, I can hear it spin when I restart the machine.

open disk utility and see if it is showing up in there if the drive is not the partition then you might be able to mount it but it could be bad and if it doesn't show up at all then yes the drive is dead.