Hi there and welcome
Can you tell me please exactly what happens when you try to log onto your account?
Thank you, ***** ***** do the following please
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
Let this complete and when it has, tell me if you still have the problem please.
ok, can you power it off.
Then hold SHIFT and keep it held and then start the computer and try to sign in.
Tell me if it then works please.
No problem and thanks
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
Turn on your Mac.
Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
Hold these keys until the computer restarts and you hear the startup sound for a second time.
Release the keys.
Does it then start?
Its the key with OPT on it, if you do not see it then you have it as the ALT key and you use that one
No, we need to attempt a reinstall.
Power off the Mac, then power it on holding command + R Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
After the Recovery menu appears, select the option to Install OS X.
Follow the onscreen prompts to select your destination disk and install OS X.
We are not erasing the hard drive so the data should be ok
Let me know the results please.
This is the problem, the hard disk has failed.
I am really sorry about this and you are going to have to return the Mac to have this replaced. It will be covered by the warranty if this has not expired, and the replacement will be done at no cost to you.
I am really sorry about this, and if you have problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service, that would be greatly appreciated.
The update wrote data to a faulty part of the hard drive which started the issue, it would have occurred regardless at a later date.
Your welcome Jan,
If you need anything else, please let me know and please remember the rating via one of the stars at the top then submit