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I have an Imac which suddenly started giving me Kernal Panics every time it boots. I suspected a hardware issue so ran a hardware test and that found no issues. I tried booting off another hard drive, several OS X installer discs from Tiger all the way to Snow Leopard and its the exact same problem. But it boots fine in Windows, all drivers installed and everything. No issues at all!

I cant work out why it always fails with OS X. If anyone can point to any ideas at all I'd really appreciate it as this is mind boggling. Thanks.

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My first suspicion for symptoms like this is a subtle RAM problem -- since OS X and Windows use RAM somewhat differently, it's plausible that it might crash consistently in one and work (almost) perfectly in the other. I've also seen flaky RAM pass "full" memory tests several times...

If you can boot OS X in single-user mode (hold command-S as it begins to boot, and it'll drop you into a very minimal command-line environment), I'd suggest running memtest on it, as I've seen it find memory problems that none of my other test utils (including the ones Apple gives service providers) would catch. Mind you, installing memtest will be a little tricky, since networking and even additional drives/partitions aren't available in single-user mode. Since it sounds like you have an external OS X boot disk, if you can mount that on another Mac, install memtest on it, and then boot the problem Mac from it, that should do it.

Another possibility is to try changing the RAM config, to remove possibly flaky RAM -- if the Mac has multiple DIMMs installed, try removing one, then the other. Try moving DIMMs between slots. If you have any spare DIMMs, try those instead of what's in the computer now.

Other things to try including booting in safe mode (hold shift as it begins to boot) -- this runs a stripped-down config with (among other things) noncritical kernel extensions disabled, so if it boots that way it may give you a some idea where the problem's coming from.

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Thanks for the ideas. I will try putting memtest on the drive and running that in single user mode. I have tried different RAM with the same results but I find Macs are a bit fussy about speeds, brands etc so it might not have liked the other RAM either. I have tried safe mode but get the same thing. A progress bar comes up under the apple logo but always get the same kernel panic at the same point around half way. I was wondering if maybe it was a firmware issue. Maybe OS X tries to access some function from the firmware which Windows doesn't touch. – Michael Jul 8 '10 at 15:25

I suggest to start from the beginning: Completely remove Windows XP (including Boot Camp), and try to install a fresh copy of OSX.

It seems like it's related to the XP in some way.

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Thanks for the reply. I should have pointed out that I've tried different hard drives etc. In the case with Windows I actually just installed it directly to a blank drive, no boot camp involved. – Michael Jul 7 '10 at 12:35
I found some site that covering a lot of Kernel panics: You should take a look and see if it can help you. – Matan Eldan Jul 7 '10 at 12:50
Thanks again, I have tried everything in there I think. I will double check. I have a few kernal panic logs and when I checked them it seemed to mention the nvidia graphics but it just seems to work so flawlessly in Windows that I dont suspect a harware issue. I could maybe post the logs later when I have access to them – Michael Jul 7 '10 at 13:11

Kernel Panics are often caused by a corrupt System folder

These two links offer some advice:

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Perhaps there's something wrong with your EFI (?). Maybe try resetting the P-RAM by holding Command + Option + P + R at boot. The Apple support article suggests doing it a couple times just to be safe. You never know; it could help! Good luck!

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