How To Reinstall Mac OS on Your Mac

You Mac does not work as well as it used to? Reinstalling Mac OS can be one of the easiest ways to fix problems on your Mac. It is not a difficult process and it does not erase your data.

See also: Mac Won’t Turn On?

Important:

!!It’s a very good idea to back up your files before attempting this because things can go wrong!! 

To back up your computer, you may have the following options:

• Time Machine (Apple menu > System Preferences > Time Machine). You can back up all of you files.
• Time Capsule
• iCloud  (System Preferences > iCloud). You can back up you photos. documents etc.
• You can also use disk utility (see below) to create a compressed back up of your files.

Here is how you can do this:

How to reinstall a new copy of Mac OS

You have two options. Option 1 (Mac Recovery mode) is to install the macOS version that was last installed on your Mac before you trying this process. Performing Option 1 will not cause any data loss. Option 2 (Mac Internet recovery mode) is to install OS X version that was originally installed on your Mac when you bought it new. Use Option 2, if you are giving away your Mac. You can also erase your data before installing Mac OS by selecting Disk Utility (see below). Also note that Both methods require that your Mac is connected to the Internet. You can decide what you want. In this article, we are using Option 1.

Here is the steps for both of them:

1. Restart your Mac or Turn on your Mac
2. Immediately after your Mac starts:
   1. For Option 1: press and hold the Command (⌘)-R keys until you see the Apple logo.
   2. For Option 2: press and hold the Option-Command-R keys until you see the Apple logo. 
   3. When you see the Apple logo, release the buttons:
3. Now you will see the utilities window.
4. Select Reinstall Mac (or Reinstall OS X) and click Continue and follow the instructions.
5. Before this, my Mac had macOS Sierra installed. So this process will reinstall macOS Sierra. 
6. Now you need to connect your Mac to the Internet. You may do so via Wi-Fi:
7. When you click, a new popup will appear saying: “To download and install mac OS, your computer’s eligibility will be verified with Apple” To verify, you need to have a Internet connection. Click Continue. 
8. After the verification step, you will be asked to agree to the terms. Click Agree to continue.
9. Next, you will select your hard drive (this is usually Macintosh HD), then click Install. 
10. You can also delete your disk, if you want to (for example; you are giving away your Mac) before reinstalling Mac OS. If you are giving away your Mac, use Option 2 because new install will not be associated with your Apple ID. If you want to do this, select Disk Utility to erase your data.

Thats it. As stated above, a fresh Mac OS installation can fix a number of common problems.

You can also restore your computer to its original factory setting.