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Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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Do I need a new GPU?


I was playing BF3 on Windows and my Imac froze. It won't reboot on Windows (black screen and then it reboots on its own). It does on Mac OS but here's what happens

Then it shuts down like that

Apple extensive hardware test doesn't find anything and the display is fine while running test or booting, but it goes crazy as soon after the apple disappears. I zapped the PRAM and the SM but nothing changed.

My theory is that the GPU (ATI 4850) is involved. It would cost me more than 600$ to have it replaced (520 euros at my local Apple premium reseller). Is my theory right? Do I need to replace the GPU? I'm not scared of trying things on my own, au contraire :) what could I try to do?

Thanks for your help

Alex from France


Hi guys,

This is what happens everytime I reboot and I repair permissions


I reboot on safe mode, some display problems remain but at least the computer is usable, even though pretty slow. When I reboot on recovery, it is extremely slow.

I cleaned all the cache with Onyx and did all the tests Onyx has to offer, but nothing was found.

I have access to a 27 Imac for the day. I booted Imac 27 with Imac 24 on target mode, everything was fine. Tried to boot Imac 24 with the 27 on target mode, all I had after the apple was a psychedelic grey screen.

Does anything make sense to you? I check the temperatures with Istat Pro and the GPU was at around 60°C (the rest around 50°).

What I don't get is how a Windows crash can affect my Mac OS X partition? Unless there's a problem with firmware and EFI but utility disk says everything's fine. Also, I cannot boot on Windows safe mode, the computer does not respond to F8 or Fn + F8.

So Machead, could you be more specific please? How would you clean cache files and preferences? Put them in the trash? And what is WinDUhoze files? Couldn't find anything about it.


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tried to restore from time machine. I had to do it with the imac 27 booting on the recovery partition of the 24. Well, it did erase my Mac OS partition, but then "an error occured during the restoration process". So now, all I have left is the non working bootcamp partition, even the recovery has been erased.


Thats not good ;-{ how far back did you go? and did you got all the way up to the last backup time point? Or did you try to create a complete fresh copy of TM on a new disk? In any case you'll need to fix your files now before moving forward, hopefully the other problem doesn't interfere with this process.


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Ouch! Nix the corruption direction, you have a hardware problem!

As I stated above todays hi-res gaming is one of the hardest things a computer can run. It pushes everything very hard. Often I see file corruption type of issues when HD's are to full or badly frag'ed. Sounds like your on top of that here - Good! Now it appears the hardware gave out under the stress.

Are you equipped into taking your system apart? If so try running Apple Hardware Test AHT again (may take a few attempts when the system is at it's hottest) to see if it can ID what needs repair/replacing. Did you get the temp monitoring software?

I suspect the GPU will need to be swapped out (given what your doing on this system), but, then again the display could also be having a problem. Otherwise you'll need to get the system to an Apple Store or Apple authorized service center.

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Puan 1

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I checked the temp after the first freeze with Istat Pro. The GPU was around 60°C. Nothing else was higher than 50°.

I managed to make a bootable USB key with Lion, and the problem remains. I'm currently writing on the iMac 27 that I brought back home which was booted on the 24 HD.

I still have my data on my time machine, but it's not accessible through the time machine interface. I'm gonna try things with Windows now, since the problem came from there.

I'll keep you posted, thanks for the support!


Well, I give up... I didn't want to erase the Bootcamp partition cause i couldn't save it. I tried to repair the partition (which had trouble mounting), it did repair many things but nothing changed. I finally found my Windows 7 DVD, it wouldn't boot up. I formated the drive, booted on a Lion USB key, and still a weird square below the mouse and long freezes. I don't want to run any more tests as I don't want to make things worse. I'll go to the Apple service center.

I'll keep you informed and tell you if it's hardware or software related, it might help somebody one day.

Thanks for trying anyway, now I know that I don't have any other choices left and that I tried everything.


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NO - I think you have a software issue with corrupt files. The fact'' that AHT runs ok points that out the HARDWARE is ok (the computer uses different set of files to run AHT). You need to access your HD from another computer and delete all the cache and preference files (first most likely location of the corrupt file(s)). You might want to clean up some of your WinDUHoze files ( a bad driver file from your crash could be the culprit).

If this answer was helpful please remember to mark it accepted.''

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I agree with Machead, you have a file corruption type of issue. Another thing you might try doing after you flush your cache files is test and then defrag the HD as it's likely the root reason you got a corruption in the first place as the file couldn't be written fast enough for the app. When the HD is badly fragmented as well as being very full your HD (without a deep onboard cache) with thrash about as it just can't find the needed blocks in contiguous locations before the cache runs out. A bigger onboard cache and faster RPM drive (7200 RPM) will improve things as well if you need to upgrade your HD.


I'll try that in a couple of days cause I don'thave access to another mac to boot on target mode atm.

I just booted on the recovery partition. There is just a display problem, I have a weird big square around the pointer. The recovery partition is supposed to be sane so... Anyway, I'm running a disk repair atm just in case. I'll keep you up to date. Thanks for the reply!


Hi Dan,

The thing is I recentely defragmented with Idefrag for the Mac partition and the Windows partition with the Windows utility programm. Could it come from that? And my HD is already a 7200rpm, with nearly 400go free (on 1to). What I don't understand is how my windows 7 partition corrupted my Mac partition. Anyway, keep you posted!


Games also run systems hotter (CPU, GPU & HD). Once the system over heats things do get unstable which is another cause. Do you have any temperature monitoring software running on your system like 'Temperature Gauge' which you can find in the App Store.


Hi, I was told that both power supply and GPU were to be replaced. No offer of trying to replace thermal paste, no explanations. Plus, I had to tell them they had my GPU wrong (even though they found it needed to be replaced).

I'm pretty sure I'm getting ripped off. 560€ for that.... What a joke.... Authorised Apple centers are complaining about Apple and Apple about them. In the end, the customer gets ripped off by both. My old parts will be shipped to Apple and I will never see them with my eyes, even though my computer is out of warranty....

My parents' Imac is a 27' with a flickering screen. I asked them about that, they told me "screen replacement, 900€". I checked youtube and fixed it myself by applying pressure...

Thanks for trying anyway and getting people more chances not to get ripped off with such a website!


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