[Atashi]

Nothing happens when I "Hold down the Command and R keys, and power the Mac back up again."

[Atashi]

And the mac is actually stuck at a blue screen. What to do?
Thanks.

[Lance666]

"...underneath it is your drive’s friendlier name."
Please don't talk down to us. That is not a "drive's friendlier name". It is a volume (formatted partition) name.

[Lance666]

"make sure that before you type "reboot" to type:
/sbin/mount -uw
Not sure what it does exactly"

There is absolutely no need to type that before reboot. If you are at the point of rebooting, you needn't do anything but reboot. The command mounts the startup volume. You need that command to see files on the volume or to apply any changes to it, such as the FSCK command to repair the volume.

[Lance666]

"Nothing happens when I "Hold down the Command and R keys, and power the Mac back up again."
Either you didn't hold the keys long enough (as much as 40 seconds for some models) or the system is pre-OS 10.7. For any older system, you boot to the DVD, not the recovery partition.

[Lance666]

"Target mode is what will run your computer into a firewire drive or usb drive,"
No, never USB. Target Disk mode only works as Firewire.

[Lance666]

"On the lower right of the Disk Utility window, click Verify Disk, and then wait while Disk Utility does its thing."
Total waste of time. The only reason to verify is if you are booted to that volume (when you cannot repair it). If you are booted to the recovery partition, as described in this article, just repair disk, never verify.

[Lance666]

"So did we waste all our time with the earlier steps? Hardly."
You absolutely did. Erasing a drive that tests error-free (after repair) in Disk Utility is a waste of time and causes unneeded terror in case the backups are not complete. Just say "No" to any "genius" who says you need to erase after DU shows no errors.

"First, we managed to get Julian’s Mac usable enough to back up crucial data. That was probably the most important step we took."
You could have backup up data without erasing the drive. Terminal can do that quite well, thank you.

"Second, all those steps ruled out numerous other issues; it was because of the freshly-wiped hard drive that the new Genius was able to conclude a logic board failure was to blame for JV’s Mac’s problems."
They could have tested with Apple Hardware Test mode and found that bad logic board. They could have booted to an external drive and gotten the hang or kernel panic. That would have confirmed a non-drive hardware issue.

I'm curious to know if the RAM was replaced at the same stage as the logic board. If so, it was probably bad RAM, and the logic board was fine.

[PhilyG]

running fsck -fy until “The volume [your Mac’s name] appears to be OK” finally works after a couple of runs.

I am a little disappointed that this kind of error would occur on a apple product.

PhilyG

[Cazza]

Amazing! I feel like Leonard from BBTheory. Thanks for the FSCK tip, 2 goes at it and my Macbook air rebooted perfectly.