About This Mac - has disappeared from iMac

Hi,

Your profile indicates your Mac is running v10.10.4. There is a v10.10.5 update available.

It may be a matter of updating OS X.

Open System Preferences > App Store then click: Check Now

First try this:

Resetting your Mac's PRAM and NVRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

Boot into Safe Mode. While in safe mode reinstall OS X.

Reinstall OS X Without Erasing the Drive

Make sure you have a current backup.

1. Restart the computer and after the chime hold down the Command and R keys until the Utility Menu appears.
2. Choose Disk Utility from the Utility Menu and click on the Continue button.
3. After Disk Utility loads select the indented (usually, Macintosh HD) entry from the side list. Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button.
4. When the process finishes, quit Disk Utility and return to the Utility Menu.
5. Select Reinstall OS X and click on the Continue button.

You will need to input the password for your Apple ID. Be sure to write it down before proceeding with the installation.

If this doesn't fix the problem, then you will need to perform an Erase and Install:

Install Yosemite orEl Capitan from Scratch

Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

1. Select Disk Utility from the Utility Menu and click on Continue button.
2. When Disk Utility loads select the volume (indented entry, usually Macintosh HD) from the side list.
3. Click on the Erase icon in Disk Utility's main window. A panel will drop down.
4. Set the Format type to Mac OS Extended (Journaled.)
5. Click on the Apply button, then wait for the Done button to activate and click on it.
6. Quit Disk Utility and return to the Utility Menu.
7. Select Reinstall OS X and click on the Continue button.

[Permission to use part or all of the above has been granted by Kappy, exclusively, to theratter.]

Try running the combo update.

10.10.5 Combo Update

Is the application 'System Information' in the /Applications/Utilities folder?

Just make a backup now. Then no matter how badly things go you can always restore your backup. The simplest way to make a backup if you don't have one is to use the Restore option in Disk Utility. Such a backup is bootable and includes a backup of the Recovery HD.

Restart the computer. After the chime press and hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears on the screen.

1. Select Disk Utility from the main menu then press the Continue

button.

2. Select the destination volume from the Devices list.

3. Click on the Restore tab in the Disk Utility main window.

4. Select the destination volume from the Devices list and drag it

to the Destination entry field.

5. Select the source volume from the Devices list and drag it to

the Source entry field.

6. Click on the Restore button.

Destination means the external backup drive. Source means the internal startup disk.

[Permission to use part or all of the above has been granted by Kappy, exclusively, to theratter.]