Stuck in setup assistant, can't login, create account, or access desktop

I am the new owner of a used MacBook Air MC966LLA. It contains existing user accounts.

When I first booted it up, I received a login screen. Not having the credentials, I booted in Single User mode to bypass the login screen.

Now every time I boot up (using the power button only), I get the Setup Assistant. Which mode is this?

So I tried to set up a new account. I can move through the setup screens just fine, until I reach the screen where you enter new account information. Every time I enter data to set up an account and press continue, I am returned to the *initial* Setup Assistant screen, not the next screen in the series.

I don't know if my problem is related to the Setup Assistant infinite loop bug, or if it is something else. I've tried all the keystroke workarounds I've been able to find in the various tech forums, but so far no luck. The Safe Mode workaround option doesn't work either, as no login screen ever appears. Just the Setup Assistant initial screen.

I have since received the login credentials from the previous owner, but I cannot return to the login screen (or any other screen) due to this stuck Setup Assistant.

Any ideas what to try next? Thanks so much for any help you can offer.

Which MacBook Air, year and model? And what version of OS X is it running?

Year and Model:
13.3-inch Apple MacBook Air MC966LL/A (Mid-2011)

Running:
Darwin 11.4.2 (Mac OS X v10.7.5) "Latest version of Lion, supplemental"

OK, thanks for posting the specs. Reboot your MBP and hold down the Command + R keys as soon as you hear the "Bong" sound. Keep holding it until it shows it's booting to the Recovery partition. If you can get into Recovery, try reinstalling Lion as long as you have the previous owner's credentials. (You'll need his Apple ID in order to reinstall.)

If the above fails or the previous owner has not given you his Apple ID, post back and we can try something else.

One problem is you do not have access to Lion from the App Store as the machine came with it. Can you get it to boot at all, open an account and Apple ID with the App Store and download Mountain Lion $19.99, make a bootable USB thumb drive and then format the drive, wiping everything, and proceed with a clean install?

I don't have access to the previous owner's AppleID. Besides, I would prefer not to wipe the disk, as there are existing user accounts (for which I now have login creds) that could be useful to me.

I asked the previous owner for any original CDs. He said there were none available.

I'm brand new to the Mac OS, and learning as fast as I can. What better way to cut one's teeth than with a debugging project... sigh.

I don't see any way around you not reinstalling. And in order to get rid of the old accounts and give you complete ownership, you should wipe the drive first. Since this is a 13" mid MBA 2011, it should have come pre-installed with Lion 10.7.2. There is no other viable way for you to get into the account unless you have the previous owner's Apple ID.

The latest Mac operating systems, Lion and Mountain Lion are only available from Apple as a download from the Mac App Store. And, as it is, you have no access to the App store without an Apple ID. What I suggest you do is call Apple customer service, explain the situation, and ask them to give you access to download Lion or Mountain Lion. Mountain Lion is only $19.99.

Better yet, if there is an Apple store nearby your home, go on in and ask them to do it for you.