Recovered my stolen Macbook, but can't log in with my user name

I assume you have no Time Machine or other backup from which to recover.

An answer depends on the OS X version that is installed.

OS X Lion: Reset a login password

OS X Mountain Lion: Reset a login password

OS X Mavericks: Reset a login password

OS X Yosemite: Reset a login password

If none of the above help read the following. When typing, do so with care. It may not work.

1. Boot single user mode.
2. You can skip the next step, but it is recommended that you do not because it will check your boot volume for errors and correct what it can:
3. At the :/ root# prompt, type fsck -fy and press Return or Enter. It will take a few moments to complete. If you are concerned that nothing is happening just press the Return key until you see the :/ root# prompt again. Once the disk check is complete and the prompt returns, type mount -uw / and press Return / Enter.
4. Type launchctl load /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist and press Enter. If you get an error message you may ignore it.
5. Type ls /Users and press Enter. All of the usernames on the computer will be listed, which is helpful if you don’t know or remember what these are.
6. Type dscl . passwd /Users/username password while replacing username with one of the users displayed in the previous step and replacing password with the new password of your choice. There is a single space before and after the . (dot) character that follows dscl. Press Enter. You will likely get an error message about a file or directory not being found. You may ignore this.
7. Type reboot and press Enter.

If you are still unsuccessful, boot OS X Recovery, erase the MBA's internal storage and reinstall OS X. That will leave it a brand new, unconfigured condition. You will need to re-create your User Accounts from the ground up.

Hopefully the thieves did not set a Firmware Password. There is no circumventing that without a trip to the Genius Bar.

Try to log in first. The presence of additional User accounts that you don't want can be dealt with later.

If you remember your short user name (if you do not, boot Single User mode to determine it using Step 5) then:

At the login screen, the one I am assuming now shows two User accounts configured by the thieves, press the key corresponding to the first letter of a User account. Which one does not matter. Just press the key and do not press Return. That will select the User account without prompting for a password (edit to add: pressing a left/right arrow key does the same thing).

Then, press the two key chord option return.

That will present two fields in which to type in your short user name and password.

Determine if you can log in using that method.

It would help if you would please provide the OS X version installed. That way, someone might be able to duplicate the problem.

msiliciano wrote:

Pressing the first letter of the user name (M, in this case) and then option+return isn't bringing up any fields, just the Mac error tone.

I can't explain that. Unfortunately I no longer have any ML systems to test but every OS X version I'm aware of had that feature. Did you try the left-right arrow keys? I added that information after posting.

The idea is to select the account icon, which will not cause the password field to appear, then option-return. The icons will disappear and two empty fields should appear.

Although I no longer have any Mountain Lion systems to test, I am nearly certain the Single User mode option above will work with it. That is if your User Account still exists and was not deleted by the thieves – I don't know how you were able to determine that.

Another option is to create a new Admin user in Single User mode, after which you can log in under that user for the purpose of deleting the unwanted accounts and possibly resurrecting your own (depends on how the thieves deleted it, assuming they did).

It would be ideal if you could back up the existing system in its entirety before messing with it. That would require another Mac and a suitable backup destination of adequate capacity. You could do that in Single User mode, eliminating the need for another Mac, but it will require a lot of typing.

Great! Thanks for the update. May the thieves enjoy a nice long vacation in jail.