Low-Level Format vs. Zero-Fill
I concur with x5dr. Most of the "low-level format" programs available from the various hard drive manufacturers are more like MID-LEVEL formats; they write hexidecimal zeros to all available sectors. In effect, they "zero-out" your recording surfaces, overwriting existing data.
A true low-level format re-writes sector marks. This means, you are re-mapping the tracks and sectors on the recording surfaces of the drive. This is the preferred method for recovering a drive with read-write errors and bad sectors. There was a time when that operation was include in the BIOS program on motherboards. That ended when hard drive capacities exceeded 512 MB and Logical Block Addressing became the norm for accessing hard drive recording space. LBA is an interpretive (logical) address-translation scheme that does not reflect the actual (physical) recording layout. The logical mask applied to a hard drive is not industry-standard; it can vary from one manufacturer to another, and probably between different-capacity drives from the same manufacturer.
The bottom line is, if the drive is physically (mechanically) damaged, it's junk; don't bother with it, other than to recover whatever data you can. If it's bad sectors, or other logical errors on a physically-healthy disk - and if you can pry the appropriate program out of the manufacturer - re-mapping your tracks and sectors is the way to go. Yes, YOU WILL LOSE EVERYTHING RECORDED ON THE DISK, so back it up first.
There is a new(ish) product on the market from Micro2000 called "EraserDisk" which claims to be able to do an honest-to-goodness track-and-sector re-mapping on any given hard drive. I'm skeptical, but I have a number of logically-crippled HD's that aren't serving any useful purpose (other than paperweights and doorstops), so I'm going to buy the disk and give it a try.
P.S. If your HD is not being recognized by the OS, the Master Boot Record has probably been corrupted. If FORMAT C: /MBR doesn't do the trick for you (and it won't if Windows doesn't recognize it as an accessible hard drive in the first place), there is an old Techie trick, involving the use of DEBUG, where you can copy the MBR from a similar drive to the dead one. I have used it to re-animate a hard drive that Windows had been reporting as a CD drive with no disk inserted.