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My 2008 iMac is having trouble booting—it never gets past the initial grey screen with the Apple logo and spinner. After letting it try to boot (spinner working) for upwards of 10 minutes, I'll get the kernel panic "You need to restart" message, then a minute later it will go black, then restart.

In addition to this, the screen has "noise" pixels all over (not dead, but graphical noise).

I've tried doing a Safe Boot (holding Shift while booting), but it never made it all the way through the boot.

I've also tried booting into single user mode, but the pixel noise all over the screen limits my ability to read the output.

Out of desperation (since nothing else was working), I did a RAM swap, but that didn't help either.

Is there another way to approach this problem?

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can you try booting off an external drive? – segiddins Oct 14 '12 at 22:04
I'll give this a try when I get back to the machine later tonight. – jasonmklug Oct 14 '12 at 22:09

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The graphical "noise" makes me think that either the graphics drivers have been corrupted (and by the sounds of it, likely more OS components), or there's a hardware defect.

  • Does the "noise" appear when the Apple logo is on screen, or just afterwards? If during the Apple logo, it's more likely a hardware problem, since that boot screen isn't based on the OS install. If afterwards, it may just be a problem with your install.
  • You can try booting off the Recovery Partition by holding down command-R when you boot.
    • If this goes well, then it's likely a problem with your boot partition being corrupted. The recovery partition includes Disk Utility, which will let you run a basic check of your boot partition, which may or may not be able to fix things.
    • If this fails, then you either have a hard drive issue, or some other hardware problem, in which case you're almost certainly going to need to consult an Apple Store or Service Provider.
  • You can also attempt to boot off an external drive as segiddins suggested in the comments.

Sorry I can't be definitive, but it's hard to say for sure without having the machine in front of me. Try some of these and let us know how it goes, and we can help narrow some things down for you.

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The noise does appear on the Apple logo screen. I actually can't get any further into the boot than that screen. Fixing a hardware issue will be probably be cost-prohibitive in this case, given how difficult iMacs are to get "into", and the fact that this is an old "spare" machine for me. – jasonmklug Oct 14 '12 at 23:13
If you can't boot any further than the Apple screen, and there are graphics issues, then I'd put my money on a hardware problem. You could try swapping in some known good RAM (one stick at a time), and see if that fixes it, but otherwise it's almost certainly a take it to the shop kind of problem. Even if you don't get it repaired, I'd suggest getting an estimate, you never know, it might be cheaper than you thought. – robmathers Oct 14 '12 at 23:17
I did the RAM swap earlier this afternoon—no luck. Good call on the hardware repair—I'll get an estimate and see where I stand. – jasonmklug Oct 14 '12 at 23:19
Did you try just one stick of RAM at a time? Possibly in different slots? I've seen cases where two sticks can cause issues, but one doesn't. Unlikely, but you never know. Otherwise, best of luck, hope it turns out to be a cheap repair bill. – robmathers Oct 14 '12 at 23:20

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