Wait until the command-line prompt appears, when all the text is done scrolling past. Then, you'll type fsck -fy and hit Return. And wait. Possibly for several long minutes.
Ideally, you'd eventually get to the "...appears to be OK" message, type reboot, and find that your Mac now starts up perfectly. Julian's Mac had other ideas.
Restore Mac OS X from Time Machine
Okay, so nothing has worked. You can use it to reinstall Mountain Lion, too. Boot into Recovery mode (hold down Command + R), and then click "Restore from a Time Machine backup" and follow the on-screen prompts.
If the restore doesn't work, you should reinstall Mac OS X completely. Boot into Recovery Mode (hold down Command + R during startup and choose "Reinstall OS X".
Follow the on screen prompts as usual until you get to the The "Do You Already Own a Mac?" window. This be used to open a program called Migration Assistant during install. Use this to restore all your files from your back. Choose the "From Time Machine backup" and click Next.
Mac OS X will be installed and the files from Time Machine will be placed back in their right order. This is a fresh installation of Mac OS X but with all your file and account information restored.
Migration Assistant is capable of restoring the following information:
- Networks and other settings
- The Applications folder
- Files and folders on "startup drive's name"
You can choose all the areas (a complete reinstall) or just the parts you want.
Reinstall Mac OS X with Time Machine without the internet
Reinstalling OS X 10.8 via Recovery HD requires an Internet connection, as the installer has to both download OS X software and verify your computer's eligibility. You can create a bootable Mountain Lion install drive . To do this, you'll need a copy of the Install Mac OS X utility from the Mac App Store. Oh, yes and you'll need to have a working Mac so if yours is currently out of order you'll need to find a friend.
One complication here is that the Install OS X utility is moved to the Trash as part of an update/install to Lion. If you plan to use it again, save the application before it gets deleted. If this advice is coming too late, you can redownload a copy from the Mac App Store (by holding down the Option key when selecting the Purchases tab).
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