I have a tendency to go off track, so I'll try to be succinct.
System: Mid-2010 (January 2011 built) iMac (Western Digital HDD, not Seagate)
Current Problem: Snow Leopard will not boot. [ ? ] folder appearing. Suspected HDD failure. No physical signs of damage, no odd sound coming from HDD when attempting to read.
Apple Care?: No, expired about 10 months ago.
Previous Problems?: Shutdown has been showing signs of slowing over the previous weeks. Blue screen with loading ring would hold for a minute before shutdown completes.
Possible Causes?: Electricity occasionally cuts in my house (surge protection used). Moving the iMac to and from a venue. Normally laid on a soft and non-vibrating surface.
Current State: Target disk showed the HDD and the original contents, HDD has been erased and reformatted using another SL machines Disk Utility.
Here's what I tried before gaining access to a second Mac, where I was then able to use Target Disk. Any attempt to communicate with the HDD from my own system resulted in Apple Logo, no cursor/load ring.
Attempt Failed: SMC Reset (No change)
Attempt: Used Verbose mode to identify that it was unable to get past the line "/system/library/extensions.mkext" followed by a line and a half of periods during boot from HDD. (Informative?)
Attemp Failed: All the other basic boot keyboard commands (pRAM, safe mode, DU etc) (No change)
Attempt Failed: Disk Warrior boot CD (results in Apple Logo, dead end)
Attemp Failed: CD Boot (Snow Leopard 10.3 Official CD, DID NOT COME WITH MY iMAC!), (results in Apple Logo, dead end)
Attempted: Hardware Testing - SATA data cable, passed (cable works fine)
Attempted: Hardware Testing - SATA power cable (works fine, plugged a long SATA data cable into a PC while powering it from the iMac. PC could recognize the drive, though MacDrive couldn't work with it at all. Ended up extracting everything I valued to the PC, which is now my only form of backup.
Today: Used FireWire and disk targeting to access the MacBook HDD of a friend. This was to prove to myself that the majority of my hardware should be ok (RAM etc) as it loaded his OS on my hardware. Obviously, this excludes anything to do with my HDD-relevant hardware (logic board, SATA data cable port, HDD).
Used the same method to access my HDD on his computer, and attempted to VERIFY (FAILED). Proceeded to attempt to REPAIR (FAILED due to many index and node errors all over the place).
ERASEd the HDD and reformatted as HFS+J (though I do not remember confirming the partition table to be GUID partition!!!!! Will confirm this by the end of tomorrow hopefully).
Attempted to VERIFY the HDD after ERASE. Success. This pushes me towards believing that it is a software error.
Attempted to boot from SL 10.3 DVD all inside my own system: Apple Logo (dead end)
Attempted to create image of the DVD to restore HDD from friend's mac using Disk Utility: Error message "Cannot validate source - resource busy". There may have been a problem with the image we created, as it would not respond to trying to load it on to my portable HDD for the sake of storage.
At this point he had to leave, so no second Mac to work with for a day or three.
Anyone got some shiny nuggets of wisdom for me? If not, and I do end up taking this to the Genius Bar, do any of you UK peeps know roughly how much it is to get a new HDD set up in a mid-2010 27" iMac? That is, assuming it's the HDD. I heard one case where it was the HDD's mounting case causing the problem...