@Jeff,

There are no known issues with those nVidia cards.  Based on my experience, I would diagnose that machine with a faulty GPU.  ASD will likely call this out.  I would visit an Apple store or AASP to get it replaced.

Cheers

Okay, I will make an appointment and report back. Thank you.

2009 iMac here with similar issues. NVIDIA GeForce GT 120 card. My iMac came with Leopard. Upgraded to Snow Leopard and never had any issues, all the way through the 10.6.x process. Upgraded to Lion, nothing but issues. I've tested hardware, repaired permissions, read through logs, uninstalled software. My graphics "flicker" and freeze when messing with a browser usually. Any browser. I recently uninstalled Parallels, Boom, and Flash. The only one i got back was Flash. Still have issues. I recently disabled wifi and went to ethernet and have had no issues freezes yet.

The ATI drivers (and NVidia drivers as others pointed out ) worked just fine up to Snow Leopard v. 10.6.2. The freezing began with the ATI drivers for my imac and others like it (the early aluminum iMacs) that shipped in 10.6.3 and subsequent versions of the Mac OS. The drivers have a bug in them that causes intermitent crashes of the video subsystem. The rest of the OS is fine, but the video sub-system is hosed. It's not widespread enough for Apple to do anything about it, but it's been misery for those of us affected by it. The only reliable solution in this instance has been to hack the operating system by replacing the new ATI drivers with the 10.6.2 drivers.

Personally, I'm running 10.7.3 with the old drivers and it's working just fine. Some times there are other problems that look like this which are GPU related, but that's kind of hard to work out. The tell tale manifestation of this problem is that the display freezes. The mouse moves but otherwise the machine is totally unresponsive. If that's what is happening for you and your machine is a late 2007/2008 imac, it's probably the post-10.6.2 ATI drivers causing your problems. Good luck with this

Ken, do you care to share with drivers you're using on 10.7.3 and how i would go about getting them to replace the current ones? I'm not sure where my Snow Leopard disk is, so i'm hoping i don't need it to try this.

Hi Jeremy,

My machine, a mid 2007 iMac, with  ATI Radeon HD 2400 XT 128 MB VRAM graphics chipset must use the 10.6.2 version of these three drivers: ATI2400Controller.kext, ATIFramebuffer.kext and ATISupport.kext. I use the "Kext Helper b7" app to update my machine with these drivers. Follow this link to an earlier page in this discussion thread. It gives step by step instructions on how to do this: 24" iMac Screen Freezes since 10.6.3...: Apple Support Communities

Thanks. Too bad, though, my graphics card isn't listed. Guess that's one good idea i can't try.

Anyone tried Mountain Lion yet? does it fix the problem? I really want my 2500$ machine back!!

I have a NVidia GT 130, and I've been trying to fix the problem since last week. I was able to do something that completely stopped the crashing. Unfortunately, what I did disabled the GPU (There was a message in the Console that says "will not use the GPU anymore), so I wasn't able to play videos (there was audio but no video) because all the operations were running on the CPU, but the machine did not crash once. I guess that's a little better.

Thanks, Apple!!!

Edit:

Is it possible to replace the video card with a different/newer model?

Is there a way to get the NVIDIA GeForce GT 120 kext file from 10.6.2 to try? All i see in the download is ATI cards.

MotaSay --

I'm wondering what you did to disable the GPU and stop the crashing.  How did you do this?  It might be at least a partial fix for other NVidia card owners...

As far as replacing the video card -- my understanding is that some iMacs have removable GPU cards and some do not.  You'll have to do some research to see which yours has.  I know my ATI GPU card is removable but I've forgotten how I determined that.  Anyway, even if yours is removable you'll probably be able to put in only the card(s) that were available when it was sold.

jeremyblake --

I've got an ATI card so I haven't paid real close attention to people's NVidia troubles, but I can't recall seeing anyone who's been able to use the "kext fix" for their NVidia card... I guess because the driver setup is different.

Brian.

@Brian

Well, I was trying to replicate the ATI fix by finding the NVidia kexts, after lots of debugging/crashing I arrived at those steps:

1. installed these kexts (taken from my 10.6.3 DVD) using the kext helper tool:

Geforce.kext

NVDANV40Hal.kext

NVDANV50Hal.kext

NVDAResman.kext

NVSMU.kext

2. Replaced these packages in Lion GeForceGLDriver.bundle and GeForceGA.plugin with the Snow Leopard version.

3. Repaired the file permissions from Disk utility.

4. Reboot.

The above steps do not fix anything. Actually its the opposite, they are breaking something that prevents the GPU from being used all together, and this in its own fixes the freezing, but prevents enjoying videos (I'm talking all videos, including YT, iTunes, etc.), some media players may play the video, but it will be very laggy (especially for HD videos) because it runs on the CPU.

My conclusion after this experiment is that the source of the problem is not the same on ATI and NVidia. Maybe I'm wrong, but I really did my best in trying to replicate the driver fix without success. Also my SL DVD has 10.6.3, and I remember using snow leopard for a long time before the freezing began, so it must have started on a later version than 10.6.3.

I'll do some research on replacing the video card. Thanks, Brian.

Update from me. I had no problems with 10.7.2 but the issue returned exactly as before with 10.7.3 (Sigh) and I hadn't kept a system backup, and it seems impossible to re-install from 10.7.3 (sigh). I tried the same fix but with 10.7.2 kexts once, but didn't fix the problem (no plans to retry!) Most GPU crashes were logged in the console.

However, the 10.6.2 kexts worked again fine, as they had with previous Lion releases.

I have also seen similar issues reported with MacBook pros. My guess is that it isn't a hardware fault, but it is a hardware/software issue - and may be changes to individual batches of ATI cards under the same revision number that the Apple drivers are not compatible with… But this does seem very unlikely - I just find it hard to believe that a hardware fault appears in a fairly random/non heat related way. And a GPU crash is regisitered. But then again, some users report it fixed with logic/graphic card replaced under AppleCare. Confused!

Because the GPU crash is not recognised by the system (~ I can still access the files from another mac on the network) then it does not give the option of "reporting to Apple". So I have (again) sent a description of my issue, referred to this thread and  pasted a part of my Console GPU crash log to http://www.apple.com/feedback/ for both the iMac and OSX options ~ noting that the 10.7.3 update still referrred to a fix for some early iMac graphic issues ~ though obviously not my one!

One thing I have never tried is plugging in a display under display mirroring? No plans to, but just wondered if anyone else had?

Has anyone tried the

iMac Graphic FW Update 3.0

that was released today? Does it install on the iMac 8,1?

I'm going to try it, but of course I won't be able to test it until I see if it hangs after a lot of use.

iMac 7,1

"Your system does not support this software"

I'm done with this issue - seriously. DONE.

No more dealing with it.

Buying new iMac.

Well, I just tried it. iMac 8,1 is not supported. A real shame, I love this iMac.

Now, should I get the 27" iMac, or the Thunderbolt display to go with my MacBook Pro....