Weird screen pattern freezes iMac, can't boot from HD or DVD

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Level 1

26 points

Weird screen pattern freezes iMac, can't boot from HD or DVD

I woke up today to find the screen of my iMac black with a sparse pattern of bright pixels on it. I wasn't able to power down holding the Power buton so I unplugged it and left it for a bit before plugging back in. I was then able reboot without any problems. Then a few hours latter a weird pattern appeared across my screen, kind of rolling, animated in spots as seen here:

I powered down, started it up and the screen had this pattern on it:

It froze during startup at the point shown in the photo with the Apple logo. I powered down, unplugged, plugged back in and then tried booting up from my Snow Leopard install disc. It also froze on the logo screen. Another attempt brought up the "You need to restart your computer…" message in different languages shown here:

I figured it was having a kernel panic so I did some searching around and followed instructions on The X Lab - Resolving Kernel Panics page and Apple's Kernel Panic Troubleshooting page. I unplugged everything but my mouse (wireless keyboard) and tried booting into Safe Mode. The screen still had the same pattern but it froze again during startup, the grey progress bar having disappeared.

I can't boot from my hard drive or from a DVD and the pattern is always on screen when I turn the iMac back on. I can't run Apple Hardware Test. I'm stuck but I'm wondering if anyone knows what the cause might be or has any suggestions on how to fix it or even get it to boot up somehow.

I have TechTool Pro and a large flash drive. I'm going to try creating a bootable USB drive with Snow Leopard on it from this backup computer and try to get TechTool Pro on it as well. I'll report back but I'd really appreciate any feedback on this problem.

iMac, Mac OS X (10.6.8), 3.06 GHz Inter Core 2 Duo, 6GB RAM

Posted on Aug 22, 2012 1:54 PM

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Answer 1

dugost Author

Level 1

26 points

Aug 23, 2012 10:54 AM in response to dugost

Some things to report. First, the night before any of this happened, I noticed the fan was running when there wasn't really any reason for it. The computer was idle, no major tasks running. I'm wondering if perhaps the videocard overheated and is causing problems. Perhaps the temperature sensors are screwed up?

Today I got a USB keyboard hooked up and reset the PRAM. Still unable to boot but the pattern on the screen did change from the mess of b&w squigglies above to vertical bars as shown here:

Trying to boot normally or in Safe Mode both result in the spinning wheel freezing and halting startup.

I found powering down then gets weird. It's like it tries to turn on again but can't after a second. Or sometimes it will and the mouse lights up, I can hear the optical drive but the screen stays dark. At that point I need to unplug and try again.

I tried booting from Snow Leopard install DVD during one of these weird cycles and could hear it trying to access the optical drive but I don't believe it even got to the chime stage.

I attempted booting from the install DVD again after unplugging. No luck there but instead of a frozen spinning wheel, it brings up the "You need to restart message…". Other methods don't do this.

Still at a loss to find a reason for this but it appears to be a hardware problem, no doubt the video card based on the screen issues. Does any of this shed any light on what the problem is or (even better) how to fix it?

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Answer 2

May 11, 2014 3:47 AM in response to dugost

I've got the exact same problem, can somebody please help.

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Answer 3

Allan Jones

Level 9

68,606 points

May 11, 2014 7:24 AM in response to Apple iMac 24"

Apple imac 24: To get effective help, please start your own post with complete details about your iMac model and OS version.

When you tag onto a thread nearly two years old, many of the experienced helpers will skip over because it is too hard to help more than one peson per thread. If you want personalized attention, you need to start a enw thread.

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Answer 4

rkaufmann87

Level 10

140,418 points

May 11, 2014 7:26 AM in response to Apple iMac 24"

Allan is correct however almost for sure your have a hardware issue that cannot be addressed on this forum. Take the machien to your local Apple Store or AASP to be professionally diagnosed.

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