macintosh HD missing from Disk utility
It is likely that the drive is toast. Disk utility is designed to see everything on any bus that looks like a drive.

You could try zapping the PRAM, or as the kids call it these days, "resetting the SMC." Google will help you find instructions for that.

Failing that you could try putting the internal drive in an external enclosure, which will mostly tell you if there is something wrong with your internal bus. There is a slim chance that this will work, allow you to format the drive and put it back in the Mac and it will work. Depends on how skilled you are with hacking around in the hardware and how much time and effort you want to put into it to test a long shot.