12 Replies Latest reply: Apr 24, 2012 8:35 AM by Lars T
Lars T Level 2 (280 points)

My iMac suddendly won't start up....kind of. It froze the other day when displaying the screensaver and now it won't boot.


It starts with the chime and the light gray screen with the Apple logo and the spinning "activity wheel".

Then the screen turns white and just stays that way. It doesn't reach the login screen.


I have tried a parameter restart, but to no avail. I have tried to boot from the original CD, but it goes straight to a kernel panic.

I have tried the hardware test from the original CD, but it says the hardware is OK. I have tried the Lion Restore disk (via startupdisk option, which works), but it also end in a blank white screen.


I have tried safeboot and it's the only way I have managed to get it started. The screen however seems low res or distorted by a wavy pattern. Almost like running in 256 color mode. When I managed to get it started I ran a permissions repair from Disk Utility, but there was no errors.

When rebooting it ends in a whiteout again.


Please advice!

iMac, Mac OS X (10.7.3), MyBook 3B
  • rkaufmann87 Level 9 (55,228 points)

    Lars T,


    I suspect you have had a hardware failure. When you ran Apple Hardware Test did you run in Extended Mode, if not that is the mode you need to try it in. Also AHT doesn't always find problems after the first pass, to be sure it should be run in Extended Mode 2-3 times to be sure. Each pass will take approximately 30-60 minutes.


    If you still don't find a problem after 3 AHT passes in Extended Mode (notice I've said that 3 times!!) then carefully and methodically follow:




    If you still don't have any luck just take it into an Apple Store or AASP to be professionally diagnosed. I'm thinking you will need to do this anyway because I suspect it's hardware.

  • Lars T Level 2 (280 points)

    Hi and thanx for the reply!


    I did try the AHT in extended mode, though one time only.

    I have now also tried to boot from an original Lion USB stick, but even this ends in a whiteout.


    I'll try another run with AHT, a few PRAM resets and finally a PMU reset before giving up.

  • rkaufmann87 Level 9 (55,228 points)

    OK, well try AHT in extended mode at least 2-3 times back to back and if still no errors used the advice letter I provided in my first post.

  • Lars T Level 2 (280 points)

    Well, have run AHT in extended mode several times now (more than 3), but finds nothing.

    Booting from CD, USB stick doesn't work. Target mode works and safe mode works, so the harddrive is working.


    Do you know what routines are run/dismissed in safe mode? Can this give a clue to what causes the problem?


    I will replace the memory modules later today with the original ones, but I don't think they are the problem.

    My guess is that there is something going on with the graphics chip. There is a wavy band pattern on the screen when in safe mode. It gets bigger when lowering the resolution. This makes me guess of a graphics chip failure rather than a display failure. Agree?

  • BDAqua Level 10 (122,227 points)

    See this great post by themachead on how to list the extensions in Safe Mode with System Profiler then compare to the extension folder!




    Indeed, most likely the Graphics Chip or VRAM, AHT ism't very good at finding errors.

  • rkaufmann87 Level 9 (55,228 points)

    I have to agree with BDAqua.

  • Lars T Level 2 (280 points)

    Status update.


    Seems I have to live with an edited system profile if I wan't it running.

    Had a chat with a certified Apple tech today. Based on what I told him about my iMac and all the things I have tried, he said I was probably 90% right about the graphics hardware problem. He also said it was one of the most common problem on old iMacs. My iMac is the last white 24'' type, making it about six years old now. So even if they could diagnose the problem an pinpoint the hardware error, they couldn't get parts for it anymore.


    He said he knew people who had heated their logic board in the oven with some luck, but don't think all go that far.


    I think the graphics chip is possible to change on these 24'' iMacs as it had the built-to-order GeForce7600. The problem is getting hold of one that works.


    Any other ideas, people?

  • rkaufmann87 Level 9 (55,228 points)



    I'd recommend looking at replacing the machine. You can look at Craigs List or EBay to see if you can find the parts you need however IMHO you are just throwing away money. Even if you can find a good one replacing it is very difficult unless you comfortable working inside a laptop which is what older iMac's are like.

  • Lars T Level 2 (280 points)

    Not quite the answer I was hoping for, but you are probably right.Thanks!

  • rkaufmann87 Level 9 (55,228 points)

    I don't know where you are located but you can check Apple's online store and see if they have refurbished units available in your area. They're a coniderable savings and you can get up-to-date models too. The link for the Refurbished USA store is: http://store.apple.com/us/browse/home/specialdeals/mac


    Good luck!

  • Lars T Level 2 (280 points)

    Thanx for the link. Maybe I shouldn't ask you this, but how do you actually make a new extension set?

    I see that themachead runs SnowLeopard. I run Lion. Is there another way to do to this in Lion?

  • Lars T Level 2 (280 points)

    Ahh...sorry, asked before I was thinking.

    I figured it out. :-)