The old way to repair such a computer was to boot from an external hard drive, that is, your version of OS X is so bad that you need to give your computer a new version to start up from to get it up and going.
That means plugging in a hard disk that contains a backup of your computer (or a new version of OS X) and running from that backup while you fix the problem.
This release means that during the roll out millions of users will be busy trying to install the new update on many devices, including desktop PCs, laptops, tablets, and (eventually) phones.
Unfortunately, even though the Anniversary Update promises to be one of the best and most stable releases, building an operating system is a very complex task, as such it's expected that some users may come across errors, bugs, and other issues during and after the installation.
This choice will keep your data, but any programs installed will be lost.
NOTE: You will need to get into the "Advanced Options" in order to get the "Refresh Option". Do not do a "Reset" as that will wipe all data you have on the laptop.
As soon as you see the rotating loading circle, press and hold the Power Button until the computer shuts off. Repeat this process a few times until you see the "Preparing Automatic Repair" screen. Now you want to let the laptop boot to the "Automatic Repair" screen. Click "Advanced Options" and then select "Troubleshoot". Here you want to select "Refresh your PC", if you do not wish to erase data, or "Reset your PC" to erase all data and restore your system. From here just follow the screen instructions until the recovery is completed.
A few days ago a update notification poped up, so I instantly installed it to see all new features etc.
In safe mode lots of ’non-essential’ things don’t work. So after you have started up into safe mode, just wait a bit, then restart. If your computer won’t even boot into safe mode then that’s more serious.
Although there could be some unknown issues during the rollout, remember that the problem is not always the operating system.
Some other factors could be causing the problem, including outdated drivers, software conflicts, or certain custom configurations.
Step 3: You see now four options for restoring from backup, reinstalling OS, using browser to search help and using disk utility. Step 4: Enter command diskutil list to find the partition where your stuff is.
In my example, it is disk0s2 with 250 GB space: Step 5: If your disk is not encrypted, enter command diskutil mount disk0s2 (if necessary, replace disk0s2 with your volume name if it is different) and go to step 7.