Boot into disk utility mac mountain lion
Then open Disk Utility, choose your hard drive and erase the drive.
Then continue installing OS X. In general, it's a good idea to wait before upgrading an operating system until the second update has been released.follow link
How do I install OS X (Mountain Lion)?
This allows bugs to be fixed and applications to be updated to run as expected on the new operating system. A major feature that debuted in Lion OS X It was called Lion Recovery under Lion.
When you install Mountain Lion or Lion, the installer creates an invisible, bootable, MB partition—a portion of a drive the operating system treats as a separate volume—on your startup drive called Recovery HD that includes a few essential utilities for fixing problems, restoring files, browsing the Web, and even reinstalling the operating system. I also cover Internet Recovery below. When you install Mountain Lion on a drive, the installer automatically attempts to repartition that drive to create the invisible Recovery HD partition.
So not everyone will get this useful feature. Your only option, according to Apple, is to back up your drive including your Boot Camp partition, if you have one , erase it repartitioning it as a single-partition, Mac OS Extended [Journaled] volume in the process , reinstall Mountain Lion or Lion, and then restore your data from your backup. Alternatively, you could install Mountain Lion on an external hard drive or thumb drive, which would create a usable Recovery HD partition on that drive. If you ever needed recovery mode, you can boot into it using that external drive or thumb drive.
Repair Boot Disk in Mac OS X with Disk Utility & Recovery HD
You can access recovery mode only when your Mac starts up, although there are two ways to do so. Keep holding these keys until you see a window with OS X Utilities in large text across the top.
Hold Option at startup, and you can choose to boot from the new Recovery HD volume. Restart or start up your Mac while holding down the Option key; keep holding Option until the Startup Manager—a gray screen showing all connected, bootable volumes—appears. One of the volumes will be called Recovery HD. OS X Recovery, also known as recovery mode, offers a number of useful troubleshooting options.
Macs released in mid or later, along with some older Macs once you install a firmware update , include a new feature called OS X Internet Recovery Lion Internet Recovery under Lion. How does Internet Recovery work? Sign up to join this community.
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If you can't start up from macOS Recovery
DavidB DavidB 2, 19 19 gold badges 54 54 silver badges 83 83 bronze badges. Select Disk Utility Select your disk on the left side. If you can't find the disk, click on the button near the top left, then select the "Show all disks" option. This will create a partition on your disk drive Quit Disk Utility and continue with installation as you did. Vladimir Prudnikov Vladimir Prudnikov 7 7 silver badges 3 3 bronze badges.