MacOS – Stuck at Apple logo during boot. Cannot enter Safe mode. Cannot use Recovery USB

bootmacosrecovery

A little background

I wanted to create a Mountain Lion recovery USB because I currently only have a Lion recovery USB. While downloading the installer image from the Mac App store, the computer froze and I had to perform a hard shutdown.

My question

I cannot boot into OSX anymore. How can I get it working again? I will try anything.

What I have tried

Entering Safe mode by holding shift on startup. But this does not seem to work. No matter how I do it.
Using the Lion recovery USB. This does not work either – I can only see a grey circle with a slash. Maybe this is happening because I have Mountain Lion installed. As I have said above, I do not have a Mountain lion recovery USB.
Contacting Apple Care / Genius bar because this Macbook Air has Apple Care. They will not help, because the Macbook Air's warranty is no longer valid as my Mac suffered from water damage not too long ago.
Downloading Mountain Lion from another Mac which only runs Lion. This is not possible in this case: The Mac App Store will only "offer" to download Mountain Lion – but when I click it the download is blocked because the Mac only runs Lion and cannot update to Mountain Lion (the Mac is too old). I should be able to download Lion at least, but have not found any option.

Best Answer

PRAM Reset

On boot, hold ⌘ cmd + ⌥ alt + P + R until the second boot chime. This can fix a variety of things including problems due to recent kernel panics.

Recovery HD

On boot, hold ⌘ cmd + R to boot into the Recovery HD. If this fails, hold ⌥ alt on boot, and select Recovery from the options available.

From here, you can open Disk Utility and select Repair Disk.

Target Disk Mode

If you wish to get information from the computer, and you have another computer and some way of connecting the two, you can boot into Target Disk Mode by holding T on boot. Files can then be taken off the drive by the other computer as if it was a normal external drive.

Internet Recovery

If you have a recent backup or Target Disk Mode worked (and your Mac is post-July 2011) you can start fresh by using Internet Recovery.

Hold ⌘ cmd + ⌥ alt + R on boot to begin. A new copy of OS X will be downloaded from the internet and installed, erasing your internal drive.

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Related Solutions

MacOS – Monitor remains grey after Apple logo during boot on Mac Pro

This happened earlier this year to a friend. The cause was disk directory damage. Upon start (during the Gray Screen of Doom) the Mac was trying to repair the damage automatically, but failing. Here's how I talked her through it.

Power down the Mac.
Boot in Safe Mode (press Power button, listen for startup tone, immediately press and hold Shift, release Shift when you see Apple logo).
Let the computer boot in Safe Mode. It may take longer than normal.
If the computer eventually reaches the desktop, simply reboot normally and see if that fixed your problem. This is the point at which this procedure worked out for my friend.
If the computer is still having problems, boot from a Mac OS X Install DVD (insert DVD, power down, restart hiding down C key).
When you reach the Installer screen, use the Utilities menu to run Disk Utility, then choose Repair Disk under the First Aid tab (if the hard disk doesn't show up in the sidebar in Disk Utility, the disk is likely irretrievably broken).

If these steps don't work, I'd suggest that you either a) Wipe the disk and do a full restore from your most recent backup; b) invest in a heavy-duty disk utility like Disk Warrior; c) take the computer to the nearest Apple Store for support help.

MacOS – How to install Mountain Lion on a disk that cannot be formatted in recovery mode

You should be able to use dd to destroy the partition's header. You can then format (erase) it and run the install.

From the installer run Terminal and type the following:

dd if=/dev/zero of=/dev/disk0s2 bs=1024 count=1024

Do be warned, this will irrecoverably destroy all data on that partition. But it looks like that's what you're expecting. Make sure you don't accidentally target the wrong thing.

Also note that I haven't done this, exactly. I've used this technique to destroy the entire partition table, not just a single partition. But I think it should work.

When you're done quit Terminal and run Disk Utility. You won't get any complaints about Core Storage.