Dead Mac in Target mode appears in Disk Utility, but not on Desktop / Finder

Do you have a USB HDD enclosure? If so put the HDD into it and plug it in to your iMac, and it should show up, if not I don't know what to do. Someone else may be able to help more.

 

Do you have a Firewire one? And a Mac that supports firewire?

 

If it shows up in Disk Utility, have you tried repairing the drive volumes? You can use Disk Utility or if that doesn't work you can try the tools on Drive Genius.

 

Beg, borrow or steal an external enclosure for the hard drive.

If you suspect the hard drive itself is failing, not just the G5, do the "freezer trick" to keep it alive for as long as it takes to clone it with your iMac.

Also, reseat your powercord on the G5, those old PSU's were touchy.

 

Is this a Power Mac G5 or an iMac G5? I assume you plan on making it functional again?

You say it got a "bit of a knock", I assume that means you physically bumped it? If you physically jerked the computer hard enough to screw up the hard drive, chances are it's ruined. Wiping/restoring will do you no good.

Assuming this is a Power Mac G5 and you plan on fixing the computer, just throw in a new hard drive in the open bay. I'd partition the new drive if you must, one section for a fresh OS install, the other for the previous HD data. Then either copy the information (if it mounts in the finder) or attempt to clone in Disk Utility. If neither of these work, you're might be SOL. DiskWarrior may be the last resort if absolutely nothing works.

As you probably know, replacement 7200rpm 3.5" SATA desktop drives are dirt cheap. Amazon sells them as cheap as ~$25. You're corrupted drive is more than likely dead from the jostle so you will have to buy a new drive anyways.

I'm not sure how much different an external USB enclosure is than accessing the drive via Target FW Disk Mode or a SATA connection. I imagine no matter the route might end up with the same result of existing in the Disk Utility but not the Finder. SATA at least is the fastest transfer speed so if the drive has minimal life left, the data will come off the fastest (require the least amount of time and wear on the HD)

Edit: I suppose the other option is grab an external drive (if you have one laying around), format it on the iMac. Use FW Target Disk Mode and Disk Utility to clone the dying drive to the external. When you get a new HD for the G5, do a fresh install and copy the documents over. This will be a much slower process though and will take longer. If your drive is on it's last legs, the less time you want to have it spend running to copy the files. I suppose there is the possibility though that with this option or the 2nd drive bay option stated earlier you could clone the mounting issue you have at hand.

Edit 2: Does a SMART status appear for the drive in Disk Utility? Also, see what happens if you press "Mount" in DU when selecting the drive (if it lets you)...

Edit 3: What OS are the two computers running? I think I remember reading sometimes OS X has issues mounting formatted drives of newer/older OS versions.

 

When the drive is connected in Target Disk mode, open Terminal and try the instructions listed here:

http://www.cnet.com/how-to/how-to-check-for-and-fix-os-x-boot-drive-errors/

Also, if you can get a utility like Tech Tool Pro or similar running that will see the drive, you can perform a disk surface scan/repair.

There's more hardcore info here - this would appear to be a last ditch attempt to copy the data bit by bit:

http://apple.stackexchange.com/questions/68838/recovering-data-off-of-a-dead-hard-drive

 

Seems like the knock has done something to the SATA ports. Unless I am mistaken the Superdrive in on an ATAPI port. Might be worth getting hold of the ASD and running diagnostics.

 

Then you'd think the OS X install disk should work as well, providing it is the correct disk for the computer in question.