Maybe the fat lady hasn't sung! The drive may have stopped due to *stiction*. If it is a desktop or tower where you can get at the drive, try tapping the drive when you start up. If it spins up you have a second chance. You can then buy a new drive assuming you have 2 or more drive bays. If it is an ATA drive configure the jumpers as *slave* and plug in the ribbon cable and power cable and try restarting it. If all goes well use disk utility to format the drive calling it something other than the name of the existing drive. When it is formatted, use CarbonCopyCloner available from http://www.versiontracker.com/macosx/ to make an exact copy of the contents of the failed drive. When finished, shut down, remove the new drive, install the jumpers as they came from the factory which is the *master* drive. Remove the old drive and install the new drive, plug in and start up. You should be back to where you were before it died with all your data. ATA drives can also fail due to a failed drive controller, attached to the drive. If it is fairly new but not under warranty you may be able to buy an exact drive and change the controller board. If that works your data should be intact. If it is under warranty perhaps your dealer will do it for you.
OTOH if you don't have a lot of data, or you have recent backups, just get a new drive. They are cheap these days.
Always remember to do regular backups. Drives will eventually fail. Be prepared.
If it is a laptop, the work is likely beyond the capabilities of a user. See an Apple Mac dealer.