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There are a few things we can try to resolve this. First, power down the computer by pressing and holding the power button until it turns off. Hold down the Shift key and turn the MacBook Air on. Keep the shift key held down. Does it make it past the Apple logo? If so, you can let it go
No, that did not work?
Correct did not work
Ok, thanks. Please power the computer back off again. This time hold the D key and turn the computer off. Any change here?
Did you mean hold the D key and turn computer on?
That did not work
Ok, only a few more to try. Let's see if we can get into single user - Turn the computer off again, this time, turn it on with Command and S held down. The screen should turn to black with white text.
The screen is black with white text
Great. What is the last thing on the screen?
The very last line
That may be cut off from the line before. What does the line just above it start with?
.Loading kernel cache file
Interesting - so it's not panicking. Ok, if you start typing - do you see it type anywhere?
Ok, so we will need to see about fixing your Mac OS X install. Please power off the computer once more. Start the computer holding down Command and R. This *should* start the recovery process. It may take awhile to boot up so give it some time.
keep holding down command andR?
Until you see the Apple logo. Give it up to about 5 minutes to boot.
It should boot to a Mac OS X Installer
nothing happening screen went blank a couple of times and returned to apple logo
Hrm. That isn't good. We can't get it to boot in safe mode (S), we can't get diagnostics to load (D), Single user booted but sounds like it froze (Command + S) and we can't get into recovery to attempt to repair the operating system (Command + R).
About how old is your MacBook Air?
5or 6 years old
Ah ok. That might've been before the internet recovery was available. Do you remember what version of Mac OS X you had on there?
I think it may be 5
Mac OS X Leopard
Do either of those sound familiar?
Ok. Do you recall having any discs with the computer?
I went through my disc files and don't have any
Sorry for my delay. Sadly, I think we may be out of options. As I explained above, none of the above tricks worked and without recovery (too early for that) and a disc, we can't repair the install of the operating system.
I think the only thing left is for you to take it to a local Apple Store to have it looked at. They can repair the install or install a fresh copy of Mac OS X onto the MacBook Air for you.
Sorry I couldn't have been more help. If you need help locating the closest Apple Store or authorized service center, please let me know.
Otherwise, please consider rating the service positively.