iMac 2011 won't boot. AHT shows no problems.

[7709876]

I'm having some issues with my 2011 model iMac this morning.

I was playing a game in Windows under bootcamp. All of a sudden the screen went all funky. It was filled with lots of wavy lines and then it went blank. I had recently reinstalled bootcamp drivers and I thought this might be an issue. I rebooted and then reinstalled the latest AMD Bootcamp drivers. I loaded the game and then got to its menu. When starting the screen went blank and the machine hung.

-I tried rebooting into Windows but it got as far as the login page before going blank and rebooting. I tried to reboot again and it got as far as the Windows logo but rebooted at this stage.
-I decided to boot into OSX to see if this was just an issue with Windows. I got as far as the progress bar. This went about 70% along before a reboot. I tried to reset the PRAM and SMC without this resolving things.
-I tried to boot into recovery. This again showed the progress bar before rebooting at around 70%.
-I tried to run the AHT. This wouldn't load so I loaded it from the net. I ran the short test and it found no faults. It is currently running the extended test as we speak.

If this shows no faults, what should I do?

As an aside, I have the AMD 6970M in this machine which Apple has a replacement programme for. Is this likely to be the culprit?

 

[7709876]

I just tried using the net based recovery startup. (CMD-OPT-R)

It seems to download it. Then I get the Apple Logo with a spinning wheel for a second. Then the screen goes blank. It then comes back with a plain grey screen and nothing else.

I had another go and before it rebooted the screen was filled with blue and black lines.

 

[Bertrude]

Sounds like your graphics card has just given up the ghost. Happened to me last month with my 2011 i7 iMac (same GPU).

Most of the time it chimed, showed the apple logo, the spinner and then a grey screen freeze. I managed to get it to boot in safe mode early on (and do some last minute back ups) but safe mode later booted and froze on a blue screen with vertical stripes/lines.

In my case I could run the Apple Hardware Test. It showed no errors regarding the graphics.

I booked an appointment at the closest genius bar and they ran a quick diagnostic test from a network drive. Told me there and then the graphics card had gone. I'd imagine they will say the same to you

 

[7709876]

Well, to update people, it was the graphics card. There was a known issue with the 6970m and I managed to get it replaced for free by Apple. (Otherwise it would have cost be £387!!)