Unexpected iMac i7 boot failure, complete with question mark folder! (Solved!)

So I fired up my beloved (late 2009) Core i7 iMac the other day, only to be served with the dreaded question mark folder of death!!!!

Don't let this happen to you!
The dreaded question mark folder of death!

The blinking question mark folder of death occurs when OS X cannot find a drive (or partition of a drive) to boot to.  It simply doesn’t know how to start up.  Apple’s support document is a good place to start, but unfortunately in my case, it simply wasn’t enough.  My iMac would never “eventually boot after a short delay”, and inserting the OS X Install DVD didn’t help.  My iMac would ignore me holding down the ‘C’ key (to force a boot from the DVD drive on a fresh power-up), and just about every other key-combination I tried – all while restarting the iMac over and over.

Finally, it occurred to me that I should try a regular USB wired keyboard instead of the bluetooth one.  Sometimes a problem such as this will hose the iMac before it is capable of acknowledging input from bluetooth peripherals, making them essentially useless when you are trying to input a button sequence before the iMac starts to boot up.  I found an extra Dell (Windows) keyboard lying around and plugged it in.  I made sure to turn off my Apple bluetooth keyboard (via holding the right-side power button until the green light turned off), and plugged in the Dell keyboard to one of the USB ports on the back of the iMac.

I tried forcing the DVD to boot again, via holding down the ‘C’ key on the keyboard, but alas, it didn’t work again!  I tried the PRAM zap key sequence as well, and that wouldn’t take either!  Finally, I turned off the iMac once more (via the power button on the back), and this time, I held the ‘Alt’ key on the Dell keyboard (this is the equivalent of the ‘option’ key on Mac keyboards), and turned on the iMac once more.  Viola! It presented me with a list of devices to boot from, one of them being my internal hard drive!!!

I selected my hard drive, and everything was normal again!  So what happened?

After some thought, I think I know exactly what caused this problem.  I had plugged in an external drive to the iMac so I could copy some files over.  Since this was pretty much the first time I was using the iMac, I had been clicking through each of the options of the System Preferences, and I distinctly remember opening the Startup Disk preferences as well.  I don’t recall altering any settings here, but I must have inadvertently de-selected my Macintosh HD as the startup disk (and probably accidentally selected the external disk, or nothing at all)!  This would effectively tell OS X, “Hey, don’t boot to the internal Macintosh HD next time!” – why OS X wouldn’t eventually boot back up to this disk, or why it would completely hose me from being able to boot directly to the OS X DVD (‘C’ key trick) is still a mystery to me.

To ensure that this never happens again, I went back into the Startup Disk preferences, selected my Macintosh HD as the startup disk, and clicked the little lock at the bottom of the settings pane to ensure I don’t ever accidentally de-select the Macintosh HD again.

What sucks is that if I didn’t have that USB keyboard lying around, I would have been screwed, because I literally tried every boot trick/key combination in the world using the Apple bluetooth keyboard, both with and without that external drive plugged in (I must have rebooted the iMac 50 times) – yet nothing worked.  There might be something ironic about an old Dell keyboard saving the day for my brand new shiny toy.  Oh well.

I hope this helps somebody else out some day!

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