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macrumors newbie
Original poster
Nov 8, 2016
Dear MacRumors Forum Users,

I’ve been helping a friend try to fix his iMac which I believe had a dodgy HDD. Machine specs below…
  • OSX 10.5.8 (Leopard)
  • 2.66 GHz Intel "Core 2 Duo" processor
  • 2 GB of RAM (1066 MHz DDR3 SDRAM)
  • 320 GB (7200 RPM) HDD
  • NVIDIA GeForce 9400M graphics
The machine essentially wouldn’t boot and the 2 hardware test message he was getting were...
  • 4MOT/1/40000003: HDD - 1458
  • 4MOT/1/40000003: HDD - 1437
I dismantled the machine to get in to the hard drive and replaced it with a new 3.5” 2TB Seagate Hybrid.

Someone gave me their bootable Snow Leopard install drive and everything appeared to install as expected, however after the machine completed the install and restarted all we’re faced with is this screen below/attached.

Now, strangely the machine boots in to Safe mode with no graphical problems which I thought might indicate an issue with the graphics card in the box. Even though Safe Mode works, I can’t run the Apple Hardware Test now.

I’ve also tried…
  • Running system updates in Safe Mode, no change after rebooting normally
  • Recovery Mode, which doesn’t load
  • Reinstalling Snow again results in the same behaviour
  • Resetting NVRAM didn’t help
So, my question is, have you seen this behaviour before and can you suggest anything to try – or is this iMac bricked!

Thank you for time and suggestions.



  • Bad Screen.png
    Bad Screen.png
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macrumors Penryn
Feb 20, 2009
Do you have the original 10.5 software install DVD that came with it?
Have you tried booting up using that?


Aug 28, 2005
My guess is that the graphics card was on its way out. This issue happened over a period of time and caused corruptions on the hard drive. You're dealing with both a dying HDD and a dying GPU.

To test the GPU, you can do the blanket trick. Power the iMac on and leave it on that screen. Put a blanket/towel over it to restrict airflow. The computer will overheat. Let it overheat for 20-30 minutes (make sure you monitor the computer). Shut it down and wait several hours for it to cool down before turning it back on.

If it works after the blanket trick, it's definitely GPU issue.


macrumors 6502a
Sep 19, 2010
+1 As the IT Sage has said, sounds like a GPU on it's last legs.

And if your friend tries to blame you for breaking his Mac, you can tell him the symptoms of a failing HDD and a failing GPU on a Mac can be similar.

Looking at that shot, I would be almost certain that it's the GPU.


macrumors newbie
Original poster
Nov 8, 2016
Apologies for the delay in reply folks.

Thanks for your responses. I think you’ve backed up my suspicions.

Time for my friend to upgrade his machine I think!

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